npm package: @ilp64/react-beautiful-dnd-r15
Description: Beautiful, accessible drag and drop for lists with React.js
Author: Alex Reardon
Latest version: 1.0.0

# react-beautiful-dnd

Beautiful, accessible drag and drop for lists with [`React.js`](https://facebook.github.io/react/)

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![example](https://raw.githubusercontent.com/alexreardon/files/master/resources/dnd.small.gif?raw=true)

## Examples 🎉

See how beautiful it is for yourself!

### Viewing on a desktop

[All the examples!](https://react-beautiful-dnd.netlify.com)

### Viewing on a mobile or tablet

- [Simple list](https://react-beautiful-dnd.netlify.com/iframe.html)
- [Board](https://react-beautiful-dnd.netlify.com/iframe.html?selectedKind=board&selectedStory=simple) - best viewed in landscape

> We provide different links for touch devices as currently [storybook](https://github.com/storybooks/storybook) does not have a good mobile menu experience [more information](https://github.com/storybooks/storybook/issues/124)

## Basic usage examples

We have created some basic examples on `codesandbox` for you to play with directly:

- [Simple vertical list](https://codesandbox.io/s/k260nyxq9v)
- [Simple horizontal list](https://codesandbox.io/s/mmrp44okvj)

> Coming soon: a getting starting guide!

## Upgrading

We have created upgrade instructions in our release notes to help you upgrade to the latest version!

- [Upgrading from `5.x` to `6.x`](https://github.com/atlassian/react-beautiful-dnd/releases/tag/v6.0.0)
- [Upgrading from `4.x` to `5.x`](https://github.com/atlassian/react-beautiful-dnd/releases/tag/v5.0.0)
- [Upgrading from `3.x` to `4.x`](https://github.com/atlassian/react-beautiful-dnd/releases/tag/v4.0.0)

## Core characteristics

- Beautiful, natural movement of items
- Clean and powerful api which is simple to get started with
- Plays extremely well with standard browser interactions
- Unopinionated styling
- No creation of additional wrapper dom nodes - flexbox and focus management friendly!
- Accessible

## Currently supported feature set

- Vertical lists ↕
- Horizontal lists ↔
- Movement between lists (▤ ↔ ▤)
- Mouse 🐭, keyboard 🎹 and touch 👉📱 (mobile, tablet and so on) support
- Auto scrolling - automatically scroll containers and the window as required during a drag (even with keyboard 🔥)
- [Multi drag support](/docs/patterns/multi-drag.md)
- Incredible screen reader support - we provide an amazing experience for english screen readers out of the box 📦. We also provide complete customisation control and internationalisation support for those who need it 💖
- Conditional [dragging](https://github.com/atlassian/react-beautiful-dnd#props-1) and [dropping](https://github.com/atlassian/react-beautiful-dnd#conditionally-dropping)
- Multiple independent lists on the one page
- Flexible item sizes - the draggable items can have different heights (vertical lists) or widths (horizontal lists)
- Custom drag handles - you can drag a whole item by just a part of it
- A `Droppable` list can be a scroll container (without a scrollable parent) or be the child of a scroll container (that also does not have a scrollable parent)
- Independent nested lists - a list can be a child of another list, but you cannot drag items from the parent list into a child list
- Server side rendering compatible
- Plays well with [nested interactive elements](https://github.com/atlassian/react-beautiful-dnd#interactive-child-elements-within-a-draggable) by default

### Lots more coming soon

You can check out all the features that will be landing soon [on our issue page](https://github.com/atlassian/react-beautiful-dnd/issues).

## Not for everyone

There are a lot of libraries out there that allow for drag and drop interactions within React. Most notable of these is the amazing [`react-dnd`](https://github.com/react-dnd/react-dnd). It does an incredible job at providing a great set of drag and drop primitives which work especially well with the [wildly inconsistent](https://www.quirksmode.org/blog/archives/2009/09/the_html5_drag.html) html5 drag and drop feature. **`react-beautiful-dnd` is a higher level abstraction specifically built for vertical and horizontal lists**. Within that subset of functionality `react-beautiful-dnd` offers a powerful, natural and beautiful drag and drop experience. However, it does not provide the breadth of functionality offered by react-dnd. So this library might not be for you depending on what your use case is.

`react-beautiful-dnd` [uses `position: fixed` to position the dragging element](#positioning-ownership). In some layouts, this might break how the element is rendered. One example is a `<table>`-based layout which will lose column widths for dragged `<tr>`s. Follow [#103](https://github.com/atlassian/react-beautiful-dnd/issues/103) for updates on support for this use case.

## Driving philosophy: physicality

The core design idea of `react-beautiful-dnd` is physicality: we want users to feel like they are moving physical objects around

### Application 1: no instant movement

It is a fairly standard drag and drop pattern for things to disappear and reappear in response to the users drag. For a more natural drag we animate the movement of items as they need to move out of the way while dragging to more clearly show a drags effect. We also animate the drop of an item so that it animates into its new home position. At no point is an item instantly moved anywhere — regardless of whether it is dragging or not.

### Application 2: knowing when to move

It is quite common for drag and drop interactions to be based on the position that user started the drag from.

In `react-beautiful-dnd` a dragging items impact is based on its centre of gravity — regardless of where a user grabs an item from. A dragging items impact follows similar rules to a set of scales ⚖️. Here are some rules that are followed to allow for a natural drag experience even with items of flexible height:

- A list is *dragged over* when the centre position of a dragging item goes over one of the boundaries of the list
- A resting drag item will move out of the way of a dragging item when the centre position of the dragging item goes over the edge of the resting item. Put another way: once the centre position of an item (A) goes over the edge of another item (B), B moves out of the way.

### Application 3: no drop shadows

Drop shadows are useful in an environment where items and their destinations snap around. However, with `react-beautiful-dnd` it should be obvious where things will be dropping based on the movement of items. This might be changed in the future - but the experiment is to see how far we can get without any of these affordances.

### Application 4: maximise interactivity

`react-beautiful-dnd` works really hard to avoid as many periods of non-interactivity as possible. The user should feel like they are in control of the interface and not waiting for an animation to finish before they can continue to interact with the interface. However, there is a balance that needs to be made between correctness and power in order to make everybody's lives more sane. Here are the only situations where some things are not interactive:

1. From when a user cancels a drag to when the drop animation completes. On cancel there are lots of things moving back to where they should be. If you grab an item in a location that is not its true home then the following drag will be incorrect.
2. Starting a drag on an item that is animating its own drop. For simplicity this is the case - it is actually quite hard to grab something while it is animating home. It could be coded around - but it seems like an edge case that would add a lot of complexity.

Keep in mind that these periods of inactivity may not always exist.

### Application 5: no drag axis locking

For now, the library does not support drag axis locking (aka drag rails). This is where the user is restricted to only dragging along one axis. The current thinking is this breaks the physical metaphor we are going for and sends a message to the user that they are interacting with a piece of software rather than moving physical objects around. It is possible to ensure that a user can only drop in a single list by using props `type` and `isDropDisabled`. You can also do some visual treatment to the list `onDragStart` to show the user that this is the only place they can interact with.

### Application 6: natural cross list movement

Rather than using an index based approach for keyboard movement between lists, `react-beautiful-dnd` performs cross list movement based on **inertia, gravity and collisions**. You can find out more about how this works by reading the blog ["Natural keyboard movement between lists"](https://medium.com/@alexandereardon/friction-gravity-and-collisions-3adac3a94e19).

![example](https://raw.githubusercontent.com/alexreardon/files/master/resources/collision.gif?raw=true)

## Carefully designed animations

With things moving a lot it would be easy for the user to become distracted by the animations or for them to get in the way. We have tweaked the various animations to ensure the right balance of guidance, performance and interactivity.

### Dropping

When you drop a dragging item its movement is based on physics (thanks [`react-motion`](https://github.com/chenglou/react-motion)). This results in the drop feeling more weighted and physical.

### Moving out of the way

Items that are moving out of the way of a dragging item do so with a CSS transition rather than physics. This is to maximise performance by allowing the GPU to handle the movement. The CSS animation curve has been designed to communicate getting out of the way.

How it is composed:

1. A warm up period to mimic a natural response time
2. A small phase to quickly move out of the way
3. A long tail so that people can read any text that is being animated in the second half of the animation

![animation curve](https://raw.githubusercontent.com/alexreardon/files/master/resources/dnd-ease-in-out-small.png?raw=true)
> animation curve used when moving out of the way

## Caring about the interaction details

### Focus management

`react-beautiful-dnd` does not create any wrapper elements. This means that it will not impact the usual tab flow of a document. For example, if you are wrapping an *anchor* tag then the user will tab to the anchor directly and not an element surrounding the *anchor*. Whatever element you wrap will be given a `tab-index` to ensure that users can tab to the element to perform keyboard dragging.

### Auto scrolling

When a user drags a `Draggable` near the edge of a *container* we automatically scroll the container as we are able to in order make room for the `Draggable`.

> A *container* is either a `Droppable` that is scrollable or has a scroll parent - or the `window`.

| Mouse and touch  | Keyboard |
| ------------------ | ---------- |
| ![auto-scroll-mouse](https://user-images.githubusercontent.com/2182637/36520373-c9e2cb7e-17e4-11e8-9e93-4d2389d51fa4.gif)  | ![auto-scroll-keyboard](https://user-images.githubusercontent.com/2182637/36520375-cc1aa45c-17e4-11e8-842d-94aed694428a.gif)  |

It also works in multi list configurations with all input types

| Mouse and touch  | Keyboard |
| ------------------ | ---------- |
| ![auto-scroll-board-mouse](https://user-images.githubusercontent.com/2182637/36520670-57752526-17e6-11e8-95b3-b5a3978a5312.gif) | ![auto-scroll-board-keyboard](https://user-images.githubusercontent.com/2182637/36520650-3d3638f8-17e6-11e8-9cba-1fb439070285.gif) |

#### For mouse and touch inputs 🐭📱

When the center of a `Draggable` gets within a small distance from the edge of a container we start auto scrolling. As the user gets closer to the edge of the container we increase the speed of the auto scroll. This acceleration uses an easing function to exponentially increase the rate of acceleration the closer we move towards the edge. We reach a maximum rate of acceleration a small distance from the true edge of a container so that the user does not need to be extremely precise to obtain the maximum scroll speed. This logic applies for any edge that is scrollable.

The distances required for auto scrolling are based on a percentage of the height or width of the container for vertical and horizontal scrolling respectively. By using percentages rather than raw pixel values we are able to have a great experience regardless of the size and shape of your containers.

##### Mouse wheel and trackpads

In addition to auto scrolling we also allow users to scroll the window or a `Droppable` manually using their *mouse wheel* or *trackpad* 👌

##### A note about big `Draggable`s

If the `Draggable` is bigger than a container on the axis you are trying to scroll - we will not permit scrolling on that axis. For example, if you have a `Draggable` that is longer than the height of the window we will not auto scroll vertically. However, we will still permit scrolling to occur horizontally.

##### iOS auto scroll shake 📱🤕

When auto scrolling on an iOS browser (webkit) the `Draggable` noticeably shakes. This is due to a [bug with webkit](https://bugs.webkit.org/show_bug.cgi?id=181954) that has no known work around. We tried for a long time to work around the issue! If you are interesting in seeing this improved please engage with the [webkit issue](https://bugs.webkit.org/show_bug.cgi?id=181954).

#### For keyboard dragging 🎹

We also correctly update the scroll position as required when keyboard dragging. In order to move a `Draggable` into the correct position we can do a combination of a `Droppable` scroll, `window` scroll and manual movements to ensure the `Draggable` ends up in the correct position in response to user movement instructions. This is boss 🔥.

This is amazing for users with visual impairments as they can correctly move items around in big lists without needing to use mouse positioning.

### Accessibility

Traditionally drag and drop interactions have been exclusively a mouse or touch interaction. This library ships with support for drag and drop interactions **using only a keyboard**. This enables power users to drive their experience entirely from the keyboard. As well as opening up these experiences to users who would have been excluded previously.

We provide **fantastic support for screen readers** to assist users with visual (or other) impairments. We ship with english messaging out of the box 📦. However, you are welcome to override these messages by using the `announce` function that it provided to all of the `DragDropContext > hook` functions.

See our [screen reader guide](docs/guides/screen-reader.md) for a guide on crafting useful screen reader messaging.

#### Example screen reader behaviour

![screen-reader-text](https://user-images.githubusercontent.com/2182637/36571009-d326d82a-1888-11e8-9a1d-e44f8b969c2f.gif)

## Mouse dragging

### Sloppy clicks and click prevention 🐱🎁

When a user presses the mouse down on an element, we cannot determine if the user was clicking or dragging. Also, sometimes when a user clicks they can move the cursor slightly — a sloppy click. So we only start a drag once the user has moved beyond a certain distance with the mouse down (the drag threshold) — more than they would if they were just making a sloppy click. If the drag threshold is not exceeded then the user interaction behaves just like a regular click. If the drag threshold is exceeded then the interaction will be classified as a drag and the standard click behaviour will not occur.

This allows consumers to wrap interactive elements such as an anchor and have it be both a standard anchor as well as a draggable item in a natural way.

(🐱🎁 is a [schrodinger's cat](https://www.youtube.com/watch?v=IOYyCHGWJq4) joke)

> To see more indepth information about how we impact standard browser events see our [how we use DOM events guide](docs/guides/how-we-use-dom-events.md)

### Keyboard shortcuts: mouse dragging

When a drag **is not occurring** `react-beautiful-dnd` does not impact any of the standard keyboard interactions (it has no listeners bound).

When a drag **is occurring** with a *mouse* the user is able to execute the following keyboard shortcuts:

- **escape** <kbd>esc</kbd> - cancel the drag

During a mouse drag the following standard keyboard events are prevented to prevent a bad experience:

- **tab** <kbd>tab ↹</kbd> - preventing tabbing
- **enter** <kbd>⏎</kbd> - preventing submission

Other than these explicitly prevented keyboard events all standard keyboard events should work as expected.

## Keyboard dragging

`react-beautiful-dnd` supports dragging with only a keyboard. We have audited how our keyboard shortcuts interact with standard browser keyboard interactions. When the user is not dragging they can use their keyboard as they normally would. While dragging we override and disable certain browser shortcuts (such as `tab`) to ensure a fluid experience for the user.

> To see more indepth information about how we impact standard browser events see our [how we use DOM events guide](docs/guides/how-we-use-dom-events.md)

### Keyboard shortcuts: keyboard dragging

When a drag is not occurring, the user will be able to navigate through the `Draggable`'s on a page using the standard **tab** <kbd>tab ↹</kbd> key to move forward through the tabbable elements and (**shift** + **tab**) (<kbd>shift</kbd> + )<kbd>tab ↹</kbd>) to move backwards. We achieve this by adding a `tab-index` to the `Draggable`. When a `Draggable` has focus the **spacebar** <kbd>space</kbd> will **lift** a `Draggable`. This will start the drag.

Once a drag is started the following keyboard shortcuts can be used:

- **spacebar** <kbd>space</kbd> - drop the `Draggable`
- **escape** <kbd>esc</kbd> - cancel the drag

The following commands are also available but they depend on the `type` of `Droppable` that the `Draggable` is *currently* in:

#### Within a vertical list

- **Up arrow** <kbd>↑</kbd> - move a `Draggable` upwards in a `Droppable`
- **Down arrow** <kbd>↓</kbd> - move a `Draggable` downwards in a `Droppable`
- **Right arrow** <kbd>→</kbd> - move a `Draggable` to a `Droppable` to the *right* of the current `Droppable` (move to new list)
- **Left arrow** <kbd>←</kbd> - move a `Draggable` to a `Droppable` to the *left* of the current `Droppable` (move to new list)

#### Within a horizontal list

- **Up arrow** <kbd>↑</kbd> - move a `Draggable` to a `Droppable` to *above* the current `Droppable` (move to new list)
- **Down arrow** <kbd>↓</kbd> - move a `Draggable` to a `Droppable` to *below* the current `Droppable` (move to new list)
- **Right arrow** <kbd>→</kbd> - move a `Draggable` to the *right* in the current `Droppable`
- **Left arrow** <kbd>←</kbd> - move a `Draggable` to the *left* in the current `Droppable`

During a drag the following standard keyboard events have their default behaviour prevented (through `event.preventDefault()`) to avoid a bad experience:

- **tab** <kbd>tab ↹</kbd> - preventing tabbing
- **enter** <kbd>⏎</kbd> - preventing submission

## Touch dragging

`react-beautiful-dnd` supports dragging on touch devices such as mobiles and tablets.

![Mobile landscape](https://github.com/alexreardon/files/blob/master/resources/iphone-landscape.gif?raw=true)

> Recorded on iPhone 6s

### Understanding intention: tap, force press, scroll and drag

When a user presses their finger (or other input) on a `Draggable` we are not sure if they where intending to *tap*, *force press*, *scroll the container* or *drag*. **As much as possible `react-beautiful-dnd` aims to ensure that a users default interaction experience remains unaffected**.

> To see more indepth information about how we impact standard browser events see our [how we use DOM events guide](docs/guides/how-we-use-dom-events.md)

### Starting a drag: long press

A user can start a drag by holding their finger 👇 on an element for a small period of time 🕑 (long press)

### Tap support

If the user lifts their finger before the timer is finished then we release the event to the browser for it to determine whether to perform the standard tap / click action. This allows you to have a `Draggable` that is both clickable such as a anchor as well as draggable. If the item was dragged then we block the tap action from occurring.

### Native scrolling support

If we detect a `touchmove` before the long press timer expires we cancel the pending drag and allow the user to scroll normally. This means that the user needs to be fairly intentional and precise with their grabbing. Once the first `touchmove` occurs we have to either opt in or out of native scrolling.

- If the long press timer **has not** expired: *allow native scrolling and prevent dragging*
- If the long press timer **has** expired: *a drag has started and we prevent native scrolling*

### Force press support

> Safari only

If the user force presses on the element before they have moved the element (even if a drag has already started) then the drag is cancelled and the standard force press action occurs. For an anchor this is a website preview.

### Vibration

> This is merely an idea - it is up to you to add this if you want this behavior.

If you like you could also trigger a [vibration event](https://developer.mozilla.org/en-US/docs/Web/API/Vibration_API) when the user picks up a `Draggable`. This can provide tactile feedback that the user is doing something. It currently is only supported in Chrome on Android.

```js
class App extends React.Component {
  onDragStart = () => {
    // good times
    if (window.navigator.vibrate) {
      window.navigator.vibrate(100);
    }
  };
  /*...*/
}
```

## Multi drag

We have created a [multi drag pattern](/docs/patterns/multi-drag.md) that you can build on top of `react-beautiful-dnd` in order to support dragging multiple `Draggable` items at once.

![multi drag demo](https://user-images.githubusercontent.com/2182637/37322724-7843a218-26d3-11e8-9ebb-8d5853387bb3.gif)

## Preset styles

We apply a number of non-visible styles to facilitate the dragging experience. We do this using combination of styling targets and techniques. It is a goal of the library to provide unopinioned styling. However, we do apply some reasonable `cursor` styling on drag handles by default. This is designed to make the library work as simply as possible out of the box. If you want to use your own cursors you are more than welcome to. All you need to do is override our cursor style rules by using a rule with [higher specificity](https://css-tricks.com/specifics-on-css-specificity/).

Here are the styles that are applied at various points in the drag lifecycle:

### In every phase

#### Always: drag handle

Styles applied to: **drag handle element** using the `data-react-beautiful-dnd-drag-handle` attribute.

A long press on anchors usually pops a content menu that has options for the link such as 'Open in new tab'. Because long press is used to start a drag we need to opt out of this behavior

```css
-webkit-touch-callout: none;
```

Webkit based browsers add a grey overlay to anchors when they are active. We remove this tap overlay as it is confusing for users. [more information](https://css-tricks.com/snippets/css/remove-gray-highlight-when-tapping-links-in-mobile-safari/).

```css
-webkit-tap-highlight-color: rgba(0,0,0,0);
```

Avoid the *pull to refresh action* and *delayed anchor focus* on Android Chrome

```css
touch-action: manipulation;
```

#### Always: Droppable

Styles applied to: **droppable element** using the `data-react-beautiful-dnd-droppable` attribute.

Opting out of the browser feature which tries to maintain the scroll position when the DOM changes above the fold. We already correctly maintain the scroll position. The automatic `overflow-anchor` behavior leads to incorrect scroll positioning post drop.

```css
overflow-anchor: none;
```

### Phase: resting

#### (Phase: resting): drag handle

Styles applied to: **drag handle element** using the `data-react-beautiful-dnd-drag-handle` attribute.

Adding a cursor style to let the user know this element is draggable. You are welcome to override this.

```css
cursor: grab;
```

### Phase: dragging

#### (Phase: dragging): drag handle element

**Styles applied using the `data-react-beautiful-dnd-drag-handle` attribute**

An optimisation to avoid processing `pointer-events` while dragging. Also used to allow scrolling through a drag handle with a track pad or mouse wheel.

```css
point-events: none;
```

#### (Phase: dragging): Draggable element

**Styles applied using the `data-react-beautiful-dnd-draggable` attribute**

This is what we use to control `Draggable`s that need to move out of the way of a dragging `Draggable`.

```css
transition: ${string};
```

**Styles applied using inline styles**

This is described by the type [`DraggableStyle`](https://github.com/atlassian/react-beautiful-dnd#type-information-1).

#### (Phase: dragging): body element

We apply a cursor while dragging to give user feedback that a drag is occurring. You are welcome to override this. A good point to do this is the `onDragStart` event.

```css
cursor: grabbing;
```

To prevent the user selecting text as they drag apply this style

```css
user-select: none;
```

### Phase: dropping

#### (Phase: dropping): drag handle element

**Styles applied using the `data-react-beautiful-dnd-drag-handle` attribute**

We apply the grab cursor to all drag handles except the drag handle for the dropping `Draggable`. At this point the user is able to drag other `Draggable`'s if they like.

```css
cursor: grab;
```

#### (Phase: dropping): draggable

Same as dragging phase

### Phase: user cancel

> When a user explicitly cancels a drag

This is the same as `Phase: dropping`. However we do not apply a `cursor: grab` to the drag handle. During a user initiated cancel we do not allow the dragging of other items until the drop animation is complete.

### Preset styles are vendor prefixed

All styles applied are vendor prefixed correctly to  meet the requirements of our [supported browser matrix](https://confluence.atlassian.com/cloud/supported-browsers-744721663.html). This is done by hand to avoid adding to react-beautiful-dnd's size by including a css-in-js library

## Installation

### Package manager

```bash
# yarn
yarn add react-beautiful-dnd

# npm
npm install react-beautiful-dnd --save
```

### Distribution bundle

A [universal module definition](https://github.com/umdjs/umd) bundle is published on `npm` under the `/dist` folder for consumption . We publish the following files:

- `dist/react-beautiful-dnd.js`
- `dist/react-beautiful-dnd.min.js` (minified bundle)

These bundles list `react` as an external which needs to be provided. This is done to reduce the size of the bundle and prevent consumers from loading `react` multiple times. You can provide `react` through your module system or simply by having `react` on the `window`.

You can use the UMD to run `react-beautiful-dnd` directly in the browser.

```html
<!-- peer dependency -->
<script src="https://unpkg.com/react@15.6.0/dist/react.js"></script>
<!-- lib (change x.x.x for the version you would like) -->
<script src="https://unpkg.com/react-beautiful-dnd@x.x.x/dist/react-beautiful-dnd.js"></script>
<!-- needed to mount your react app -->
<script src="https://unpkg.com/react-dom@15.6.0/dist/react-dom.js"></script>

<script>
  const React = window.React;
  const ReactDOM = window.ReactDOM;
  const { DragDropContext, Draggable, Droppable } = window.ReactBeautifulDnd;

  class App extends React.Component {
    //...
  }

  // You can use JSX if your environment supports it
  ReactDOM.render(React.createElement(App), document.getElementById('app'));
</script>
```

There is also an [example codepen](https://codepen.io/alexreardon/project/editor/ZyNMPo) you can use to play with this installation method.

## [`ClojureScript`](https://clojurescript.org/)

You can consume `react-beautiful-dnd` from within `ClojureScript` using [CLJSJS](https://cljsjs.github.io/)!

## API

Okay, into the fun stuff - so how do you use the library?

## `DragDropContext`

In order to use drag and drop, you need to have the part of your `React` tree that you want to be able to use drag and drop in wrapped in a `DragDropContext`. It is advised to just wrap your entire application in a `DragDropContext`. Having nested `DragDropContext`'s is *not* supported. You will be able to achieve your desired conditional dragging and dropping using the props of `Droppable` and `Draggable`. You can think of `DragDropContext` as having a similar purpose to the [react-redux Provider component](https://github.com/reactjs/react-redux/blob/master/docs/api.md#provider-store)

### Props

```js
type Hooks = {|
  // optional
  onDragStart?: OnDragStartHook,
  onDragUpdate?: OnDragUpdateHook,
  // always required
  onDragEnd: OnDragEndHook,
|}

type OnDragStartHook = (start: DragStart, provided: HookProvided) => void;
type OnDragUpdateHook = (update: DragUpdate, provided: HookProvided) => void;
type OnDragEndHook = (result: DropResult, provided: HookProvided) => void;

type Props = {|
  ...Hooks,
  children: ?Node,
|}
```

### Basic usage

```js
import { DragDropContext } from 'react-beautiful-dnd';

class App extends React.Component {
  onDragStart = () => {
    /*...*/
  };
  onDragUpdate = () => {
    /*...*/
  }
  onDragEnd = () => {
    // the only one that is required
  };

  render() {
    return (
      <DragDropContext
        onDragStart={this.onDragStart}
        onDragUpdate={this.onDragUpdate}
        onDragEnd={this.onDragEnd}
      >
        <div>Hello world</div>
      </DragDropContext>
    );
  }
}
```

### `Hook`s

These are top level application events that you can use to perform your own state updates as well as to make screen reader announcements. For more information about controlling the screen reader see our [screen reader guide](docs/guides/screen-reader.md)

### `provided: HookProvided`

```js
type HookProvided = {|
  announce: Announce,
|}

type Announce = (message: string) => void;
```

All hooks are provided with a second argument: `HookProvided`. This object has one property: `announce`. This function is used to synchronously announce a message to screen readers. If you do not use this function we will announce a default english message. We have created a [guide for screen reader usage](docs/guides/screen-reader.md) which we recommend using if you are interested in controlling the screen reader messages for yourself and to support internationalisation. If you are using `announce` it must be called synchronously.

### `onDragStart` (optional)

```js
type OnDragStartHook = (start: DragStart, provided: HookProvided) => void;
```

`onDragStart` will get notified when a drag starts. This hook is *optional* and therefore does not need to be provided. It is **highly recommended** that you use this function to block updates to all `Draggable` and `Droppable` components during a drag. (See [*Best practices for `hooks` *](https://github.com/atlassian/react-beautiful-dnd#best-practices-for-hooks))

You are provided with the following details:

#### `start: DragStart`

```js
type DragStart = {|
  draggableId: DraggableId,
  type: TypeId,
  source: DraggableLocation,
|}
```

- `start.draggableId`: the id of the `Draggable` that is now dragging
- `start.type`: the `type` of the `Draggable` that is now dragging
- `start.source`: the location (`droppableId` and `index`) of where the dragging item has started within a `Droppable`.

#### `onDragStart` type information

```js
type OnDragStartHook = (start: DragStart, provided: HookProvided) => void;

// supporting types
type DragStart = {|
  draggableId: DraggableId,
  type: TypeId,
  source: DraggableLocation,
|}

type DraggableLocation = {|
  droppableId: DroppableId,
  // the position of the draggable within a droppable
  index: number
|};
type Id = string;
type DraggableId = Id;
type DroppableId = Id;
type TypeId = Id;
```

### `onDragUpdate` (optional)

```js
type OnDragUpdateHook = (update: DragUpdate, provided: HookProvided) => void;
```

This hook is called whenever something changes during a drag. The possible changes are:

- The position of the `Draggable` has changed
- The `Draggable` is now over a different `Droppable`
- The `Draggable` is now over no `Droppable`

It is important that you not do too much work as a result of this function as it will slow down the drag.

#### `update: DragUpdate`

```js
type DragUpdate = {|
  ...DragStart,
  // may not have any destination (drag to nowhere)
  destination: ?DraggableLocation,
|}
```

- `update.draggableId`: the id of the `Draggable` that is now dragging
- `update.type`: the `type` of the `Draggable` that is now dragging
- `update.source`: the location (`droppableId` and `index`) of where the dragging item has started within a `Droppable`.
- `update.destination`: the location (`droppableId` and `index`) of where the dragging item is now. This can be null if the user is currently not dragging over any `Droppable`.

### `onDragEnd` (required)

This function is *extremely* important and has an critical role to play in the application lifecycle. **This function must result in the *synchronous* reordering of a list of `Draggables`**

It is provided with all the information about a drag:

#### `result: DropResult`

```js
type DropResult = {|
  ...DragUpdate,
  reason: DropReason,
|}

type DropReason = 'DROP' | 'CANCEL';
```

- `result.draggableId`: the id of the `Draggable` that was dragging.
- `result.type`: the `type` of the `Draggable` that was dragging.
- `result.source`: the location where the `Draggable` started.
- `result.destination`: the location where the `Draggable` finished. The `destination` will be `null` if the user dropped while not over a `Droppable`.
- `result.reason`: the reason a drop occurred. This information can be helpful in crafting more useful messaging in the `HookProvided` > `announce` function.

### Synchronous reordering

Because this library does not control your state, it is up to you to *synchronously* reorder your lists based on the `result: DropResult`.

#### Here is what you need to do

- if the `destination` is `null`: all done!
- if `source.droppableId` equals `destination.droppableId` you need to remove the item from your list and insert it at the correct position.
- if `source.droppableId` does not equal `destination.droppableId`, then you need to remove the `Draggable` from the `source.droppableId` list and add it into the correct position of the `destination.droppableId` list.

### Persisting a reorder

If you need to persist a reorder to a remote data store - update the list synchronously on the client and fire off a request in the background to persist the change. If the remote save fails it is up to you how to communicate that to the user and update, or not update, the list.

### Best practices for `hooks`

#### Block updates during a drag

It is **highly** recommended that while a user is dragging that you block any state updates that might impact the amount of `Draggable`s and `Droppable`s, or their dimensions. Please listen to `onDragStart` and block updates to the `Draggable`s and `Droppable`s until you receive at `onDragEnd`.

When the user starts dragging we take a snapshot of all of the dimensions of the applicable `Draggable` and `Droppable` nodes. If these change during a drag we will not know about it.

Here are a few poor user experiences that can occur if you change things *during a drag*:

- If you increase the amount of nodes, then the library will not know about them and they will not be moved when the user would expect them to be.
- If you decrease the amount of nodes, then there might be gaps and unexpected movements in your lists.
- If you change the dimensions of any node, then it can cause the changed node as well as others to move at incorrect times.
- If you remove the node that the user is dragging, then the drag will instantly end
- If you change the dimension of the dragging node, then other things will not move out of the way at the correct time.

#### Force focus after a transition between lists

When an item is moved from one list to a different list, it loses browser focus if it had it. This is because `React` creates a new node in this situation. It will not lose focus if transitioned within the same list. The dragging item will always have had browser focus if it is dragging with a keyboard. It is highly recommended that you give the item (which is now in a different list) focus again. You can see an example of how to do this in our stories. Here is an example of how you could do it:

- `onDragEnd`: move the item into the new list and record the id of the item that has moved
- When rendering the reordered list, pass down a prop which will tell the newly moved item to obtain focus
- In the `componentDidMount` lifecycle call back check if the item needs to gain focus based on its props (such as an `autoFocus` prop)
- If focus is required - call `.focus` on the node. You can obtain the node by using `ReactDOM.findDOMNode` or monkey patching the `provided.innerRef` callback.

### `onDragStart` and `onDragEnd` pairing

We try very hard to ensure that each `onDragStart` event is paired with a single `onDragEnd` event. However, there maybe a rogue situation where this is not the case. If that occurs - it is a bug. Currently there is no mechanism to tell the library to cancel a current drag externally.

## `Droppable`

`Droppable` components can be **dropped on by a `Draggable`**. They also **contain** `Draggable`s. A `Draggable` must be contained within a `Droppable`.

```js
import { Droppable } from 'react-beautiful-dnd';

<Droppable droppableId="droppable-1" type="PERSON">
  {(provided, snapshot) => (
    <div
      ref={provided.innerRef}
      style={{ backgroundColor: snapshot.isDraggingOver ? 'blue' : 'grey' }}
      {...provided.droppableProps}
    >
      <h2>I am a droppable!</h2>
      {provided.placeholder}
    </div>
  )}
</Droppable>;
```

### Droppable props

- `droppableId`: A *required* `DroppableId(string)` that uniquely identifies the droppable for the application. Please do not change this prop - especially during a drag.
- `type`: An *optional* `TypeId(string)` that can be used to simply accept a class of `Draggable`. For example, if you use the type `PERSON` then it will only allow `Draggable`s of type `PERSON` to be dropped on itself. `Draggable`s of type `TASK` would not be able to be dropped on a `Droppable` with type `PERSON`. If no `type` is provided, it will be set to `'DEFAULT'`. Currently the `type` of the `Draggable`s within a `Droppable` **must be** the same. This restriction might be loosened in the future if there is a valid use case.
- `isDropDisabled`: An *optional* flag to control whether or not dropping is currently allowed on the `Droppable`. You can use this to implement your own conditional dropping logic. It will default to `false`.
- `direction`: The direction in which items flow in this droppable. Options are `vertical` (default) and `horizontal`.
- `ignoreContainerClipping`: When a `Droppable` is inside a scrollable container its area is constrained so that you can only drop on the part of the `Droppable` that you can see. Setting this prop opts out of this behavior, allowing you to drop anywhere on a `Droppable` even if it's visually hidden by a scrollable parent. The default behavior is suitable for most cases so odds are you'll never need to use this prop, but it can be useful if you've got very long `Draggable`s inside a short scroll container. Keep in mind that it might cause some unexpected behavior if you have multiple `Droppable`s inside scroll containers on the same page.

### Children function

The `React` children of a `Droppable` must be a function that returns a [`ReactElement`](https://tylermcginnis.com/react-elements-vs-react-components/).

```js
<Droppable droppableId="droppable-1">
  {(provided, snapshot) => ({
    /*...*/
  })}
</Droppable>;
```

The function is provided with two arguments:

#### 1. provided: (DroppableProvided)**

```js
type DroppableProvided = {|
  innerRef: (?HTMLElement) => void,
  droppableProps: DroppableProps,
  placeholder: ?ReactElement,
|}

type DroppableProps = {|
  // used for shared global styles
  'data-react-beautiful-dnd-droppable': string,
|}
```

- `provided.innerRef`: In order for the droppable to function correctly, **you must** bind the `provided.innerRef` to the highest possible DOM node in the `ReactElement`. We do this in order to avoid needing to use `ReactDOM` to look up your DOM node. *This prop is planned to be removed when we move to React 16*
- `provided.placeholder`: This is used to create space in the `Droppable` as needed during a drag. This space is needed when a user is dragging over a list that is not the home list. Please be sure to put the placeholder inside of the component for which you have provided the ref. We need to increase the size of the `Droppable` itself. This is different from `Draggable` where the `placeholder` needs to be a *sibling* to the draggable node.
- `provided.droppableProps (DroppableProps)`: This is an Object that contains properties that need to be applied to a Droppable element. It needs to be applied to the same element that you apply `provided.innerRef` to. It currently contains a `data` attribute that we use to control some non-visible css.

```js
<Droppable droppableId="droppable-1">
  {(provided, snapshot) => (
    <div ref={provided.innerRef} {...provided.droppableProps}>
      Good to go

      {provided.placeholder}
    </div>
  )}
</Droppable>;
```

#### 2. snapshot: (DroppableStateSnapshot)**

```js
type DroppableStateSnapshot = {|
  // Is the Droppable being dragged over?
  isDraggingOver: boolean,
  // What is the id of the draggable that is dragging over the Droppable?
  draggingOverWith: ?DraggableId,
|};
```

The `children` function is also provided with a small amount of state relating to the current drag state. This can be optionally used to enhance your component. A common use case is changing the appearance of a `Droppable` while it is being dragged over.

```js
<Droppable droppableId="droppable-1">
  {(provided, snapshot) => (
    <div
      ref={provided.innerRef}
      style={{ backgroundColor: snapshot.isDraggingOver ? 'blue' : 'grey' }}
      {...provided.droppableProps}
    >
      I am a droppable!

      {provided.placeholder}
    </div>
  )}
</Droppable>;
```

### Conditionally dropping

- `Droppable`s can only be dropped on by `Draggable`s who share the same `type`. This is a simple way of allowing conditional dropping. If you do not provide a `type` for the `Droppable`, then it will only accept `Draggable`s which also have the default type. `Draggable`s and `Droppable`s both will have their `types` set to `'DEFAULT'` when none is provided. There is currently no way to set multiple `types`, or a `type` wildcard that will accept `Draggable`s of multiple any types. This could be added if there is a valid use case.
- Using the `isDropDisabled` prop you can conditionally allow dropping. This allows you to do arbitrarily complex conditional transitions. This will only be considered if the `type` of the `Droppable` matches the `type` of the currently dragging `Draggable`.
- You can disable dropping on a `Droppable` altogether by always setting `isDropDisabled` to false. You can do this to create a list that is never able to be dropped on, but contains `Draggable`s.
- Technically you do not need to use `type` and do all of your conditional drop logic with the `isDropDisabled` function. The `type` parameter is a convenient shortcut for a common use case.

### Scroll containers

This library supports dragging within scroll containers (DOM elements that have `overflow: auto;` or `overflow: scroll;`). The **only** supported use cases are:

1. The `Droppable` can itself be a scroll container with **no scrollable parents**
2. The `Droppable` has **one scrollable parent**

where a *scrollable parent* refers to a scroll container that is not the window itself.

### Empty `Droppable`s

It is recommended that you put a `min-height` on a vertical `Droppable` or a `min-width` on a horizontal `Droppable`. Otherwise when the `Droppable` is empty there may not be enough of a target for `Draggable` being dragged with touch or mouse inputs to be *over* the `Droppable`.

### Recommended Droppable performance optimisation

When a user drags over, or stops dragging over, a `Droppable` we re-render the `Droppable` with an updated `DroppableStateSnapshot > isDraggingOver` value. This is useful for styling the `Droppable`. However, by default this will cause a render of all of the children of the `Droppable` - which might be 100's of `Draggable`s! This can result in a noticeable frame rate drop. To avoid this problem we recommend that you create a component that is the child of a `Droppable` who's responsibility it is to avoid rendering children if it is not required.

Here is an example of how you could do this:

```js
import React, { Component } from 'react';

class Student extends Component<{ student: Person }> {
  render() {
    // Renders out a draggable student
  }
}

class InnerList extends Component<{ students: Person[] }> {
  // do not re-render if the students list has not changed
  shouldComponentUpdate(nextProps: Props) {
    if(this.props.students === nextProps.students) {
      return false;
    }
    return true;
  }
  // You could also not do your own shouldComponentUpdate check and just
  // extend from React.PureComponent

  render() {
    return this.props.students.map((student: Person) => (
      <Student student={student} />
    ))
  }
}

class Students extends Component {
  render() {
    return (
      <Droppable droppableId="list">
        {(provided: DroppableProvided, snapshot: DroppableStateSnapshot) => (
          <div
            ref={provided.innerRef}
            style={{ backgroundColor: provided.isDragging ? 'green' : 'lightblue' }}
            {...provided.droppableProps}
          >
            <InnerList students={this.props.students} />
            {provided.placeholder}
          </div>
        )}
      </Droppable>
    )
  }
}
```

By using the approach you are able to make style changes to a `Droppable` when it is being dragged over, but you avoid re-rendering all of the children unnecessarily. Keep in mind that if you are using `React.PureComponent` that your component will [not respond to changes in the context](https://github.com/facebook/react/issues/2517).

Unfortunately we are [unable to apply this optimisation for you](https://medium.com/merrickchristensen/function-as-child-components-5f3920a9ace9). It is a byproduct of using the function-as-child pattern.

## `Draggable`

`Draggable` components can be dragged around and dropped onto `Droppable`s. A `Draggable` must always be contained within a `Droppable`. It is **possible** to reorder a `Draggable` within its home `Droppable` or move to another `Droppable`. It is **possible** because a `Droppable` is free to control what it allows to be dropped on it.

Every `Draggable` has a *drag handle*. A *drag handle* is the element that the user interacts with in order to drag a `Draggable`. A *drag handle* can be a the `Draggable` element itself, or a child of the `Draggable`.

```js
import { Draggable } from 'react-beautiful-dnd';

<Draggable draggableId="draggable-1" type="PERSON" index={0}>
  {(provided, snapshot) => (
    <div>
      <div
        ref={provided.innerRef}
        {...provided.draggableProps}
        {...provided.dragHandleProps}
      >
        <h4>My draggable</h4>
      </div>
      {provided.placeholder}
    </div>
  )}
</Draggable>;
```

> Note: when the library moves to React 16 this will be cleaned up a little bit as we will be able to return the placeholder as a sibling to your child function without you needing to create a wrapping element

### Draggable Props

- `draggableId`: A *required* `DraggableId(string)` that uniquely identifies the `Draggable` for the application. Please do not change this prop - especially during a drag.
- `index`: A *required* `number` that matches the order of the `Draggable` in the `Droppable`. It is simply the index of the `Draggable` in the list. The `index` needs to be unique within a `Droppable` but does not need to be unique between `Droppables`. Typically the `index` value will simply be the `index` provided by a `Array.prototype.map` function:

```js
{this.props.items.map((item, index) => (
  <Draggable draggableId={item.id} index={index}>
    {(provided, snapshot) => (
      <div>
        <div ref={provided.innerRef} {...provided.draggableProps}>
          {item.content}
        </div>
      </div>
    )}
  </Draggable>
))}
```

- `type`: An *optional* type (`TypeId(string)`) of the `Draggable`. This is used to control what `Droppable`s the `Draggable` is permitted to drop on. `Draggable`s can only drop on `Droppable`s that share the same `type`. If no `type` is provided, then it will be set to `'DEFAULT'`. Currently the `type` of a `Draggable` **must be** the same as its container `Droppable`. This restriction might be loosened in the future if there is a valid use case.
- `isDragDisabled`: An *optional* flag to control whether or not the `Draggable` is permitted to drag. You can use this to implement your own conditional drag logic. It will default to `false`.
- `disableInteractiveElementBlocking`: An *optional* flag to opt out of blocking a drag from interactive elements. For more information refer to the section *Interactive child elements within a `Draggable`*

### Children function

The `React` children of a `Draggable` must be a function that returns a `ReactElement`.

```js
<Draggable draggableId="draggable-1" index={0}>
  {(provided, snapshot) => (
    <div>
      <div
        ref={provided.innerRef}
        {...provided.draggableProps}
        {...provided.dragHandleProps}
      >
        Drag me!
      </div>
      {provided.placeholder}
    </div>
  )}
</Draggable>;
```

The function is provided with two arguments:

#### 1. provided: (DraggableProvided)**

```js
type DraggableProvided = {|
  innerRef: (HTMLElement) => void,
  draggableProps: DraggableProps,
  // will be null if the draggable is disabled
  dragHandleProps: ?DragHandleProps,
  // null if not required
  placeholder: ?ReactElement,
|}
```

Everything within the *provided* object must be applied for the `Draggable` to function correctly.

- `provided.innerRef (innerRef: (HTMLElement) => void)`: In order for the `Droppable` to function correctly, **you must** bind the `innerRef` function to the `ReactElement` that you want to be considered the `Draggable` node. We do this in order to avoid needing to use `ReactDOM` to look up your DOM node.

##### `innerRef` Example

```js
<Draggable draggableId="draggable-1" index={0}>
  {(provided, snapshot) => <div ref={provided.innerRef}>Drag me!</div>}
</Draggable>;
```

- `provided.draggableProps (DraggableProps)`: This is an Object that contains a `data` attribute and an inline `style`. This Object needs to be applied to the same node that you apply `provided.innerRef` to. This controls the movement of the draggable when it is dragging and not dragging. You are welcome to add your own styles to `DraggableProps.style` – but please do not remove or replace any of the properties.

##### `draggableProps` Type information

```js
// Props that can be spread onto the element directly
export type DraggableProps = {|
  // inline style
  style: ?DraggableStyle,
  // used for shared global styles
  'data-react-beautiful-dnd-draggable': string,
|}

type DraggableStyle = DraggingStyle | NotDraggingStyle
type DraggingStyle = {|
  position: 'fixed',
  width: number,
  height: number,
  boxSizing: 'border-box',
  pointerEvents: 'none',
  top: number,
  left: number,
  margin: 0,
  transition: 'none',
  transform: ?string,
  zIndex: ZIndex,
|}
type NotDraggingStyle = {|
  transition: ?string,
  transition: null | 'none',
|}
```

##### `draggableProps` Example

```js
<Draggable draggableId="draggable-1" index={0}>
  {(provided, snapshot) => (
    <div>
      <div ref={provided.innerRef} {...provided.draggableProps}>
        Drag me!
      </div>
    </div>
  )}
</Draggable>;
```

##### Positioning ownership

It is a contract of this library that it owns the positioning logic of the dragging element. This includes properties such as `top`, `right`, `bottom`, `left` and `transform`. The library may change how it positions things and which properties it uses without performing a major version bump. It is also recommended that you do not apply your own `transition` property to the dragging element.

##### Warning: `position: fixed`

`react-beautiful-dnd` uses `position: fixed` to position the dragging element. This is quite robust and allows for you to have `position: relative | absolute | fixed` parents. However, unfortunately `position:fixed` is [impacted by `transform`](http://meyerweb.com/eric/thoughts/2011/09/12/un-fixing-fixed-elements-with-css-transforms/) (such as `transform: rotate(10deg);`). This means that if you have a `transform: *` on one of the parents of a `Draggable` then the positioning logic will be incorrect while dragging. Lame! For most consumers this will not be an issue.

This will be changing soon as we move to a [portal solution](https://github.com/atlassian/react-beautiful-dnd/issues/192) where we will be appending the `Draggable` to the end of the body to avoid any parent transforms. If you really need this feature right now we have [created an example](https://www.webpackbin.com/bins/-L-3aZ_bTMiGPl8bqlRB) where we implement a portal on top of the current api. Please note however, this technique is not officially supported and might break in minor / patch releases.

##### Extending `DraggableProps.style`

If you are using inline styles you are welcome to extend the `DraggableProps.style` object. You are also welcome to apply the `DraggableProps.style` object using inline styles and use your own styling solution for the component itself - such as [styled-components](https://github.com/styled-components/styled-components).

If you are overriding inline styles be sure to do it after you spread the `provided.draggableProps` or the spread will override your inline style.

```js
<Draggable draggable="draggable-1" index={0}>
  {(provided, snapshot) => {
    // extending the DraggableStyle with our own inline styles
    const style = {
      backgroundColor: snapshot.isDragging ? 'blue' : 'white',
      fontSize: 18,
      ...provided.draggableProps.style,
    };
    return (
      <div>
        <div
          ref={provided.innerRef}
          {...provided.draggableProps}
          style={style}
        >
          Drag me!
        </div>
      </div>
    );
  }}
</Draggable>;
```

##### Avoid margin collapsing between `Draggable`s

[margin collapsing](https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_Box_Model/Mastering_margin_collapsing) is one of those really hard parts of CSS. For our purposes, if you have one `Draggable` with a `margin-bottom: 10px` and the next `Draggable` has a `margin-top: 12px` these margins will *collapse* and the resulting margin will be the greater of the two: `12px`. When we do our calculations we are currently not accounting for margin collapsing. If you do want to have a margin on the siblings, wrap them both in a `div` and apply the margin to the inner `div` so they are not direct siblings.

##### `Draggable`s should be visible siblings

It is an assumption that `Draggable`s are *visible siblings* of one another. There can be other elements in between, but these elements should not take up any additional space. You probably will not do this anyway, but just calling it out to be super clear.

```js
// Direct siblings ✅
<Draggable draggableId="draggable-1" index={0}>
  {() => {}}
</Draggable>
<Draggable draggableId="draggable-2" index={1}>
  {() => {}}
</Draggable>

// Not direct siblings, but are visible siblings ✅
<div>
  <Draggable draggableId="draggable-1" index={0}>
    {() => {}}
  </Draggable>
</div>
<div>
  <Draggable draggableId="draggable-2" index={1}>
    {() => {}}
  </Draggable>
</div>

// Spacer elements ❌
<Draggable draggableId="draggable-1" index={0}>
    {() => {}}
</Draggable>
<p>I will break things!</p>
<Draggable draggableId="draggable-2" index={1}>
    {() => {}}
</Draggable>

// Spacing on non sibling wrappers ❌
<div style={{padding: 10}}>
  <Draggable draggableId="draggable-1" index={0}>
    {() => {}}
  </Draggable>
</div>
<div style={{padding: 10}}>
  <Draggable draggableId="draggable-2" index={1}>
    {() => {}}
  </Draggable>
</div>
```

- `provided.dragHandleProps (?DragHandleProps)` every `Draggable` has a *drag handle*. This is what is used to drag the whole `Draggable`. Often this will be the same node as the `Draggable`, but sometimes it can be a child of the `Draggable`. `DragHandleProps` need to be applied to the node that you want to be the drag handle. This is a number of props that need to be applied to the `Draggable` node. The simplest approach is to spread the props onto the draggable node (`{...provided.dragHandleProps}`). However, you are also welcome to [monkey patch](https://davidwalsh.name/monkey-patching) these props if you also need to respond to them. DragHandleProps will be `null` when `isDragDisabled` is set to `true`.

##### `dragHandleProps` Type information

```js
type DragHandleProps = {|
  onMouseDown: (event: MouseEvent) => void,
  onKeyDown: (event: KeyboardEvent) => void,
  onTouchStart: (event: TouchEvent) => void,
  onTouchMove: (event: TouchEvent) => void,
  'data-react-beautiful-dnd-drag-handle': string,
  'aria-roledescription': string,
  tabIndex: number,
  draggable: boolean,
  onDragStart: (event: DragEvent) => void,
|}
```

##### `dragHandleProps` Example: standard

```js
<Draggable draggableId="draggable-1" index={0}>
  {(provided, snapshot) => (
    <div>
      <div
        ref={provided.innerRef}
        {...provided.draggableProps}
        {...provided.dragHandleProps}
      >
        Drag me!
      </div>
      {provided.placeholder}
    </div>
  )}
</Draggable>;
```

##### `dragHandleProps` Example: custom drag handle

Controlling a whole draggable by just a part of it

```js
<Draggable draggableId="draggable-1" index={0}>
  {(provided, snapshot) => (
    <div>
      <div ref={provided.innerRef} {...provided.draggableProps}>
        <h2>Hello there</h2>
        <div {...provided.dragHandleProps}>Drag handle</div>
      </div>
      {provided.placeholder}
    </div>
  )}
</Draggable>;
```

##### `dragHandleProps` monkey patching

You can override some of the `dragHandleProps` props with your own behavior if you need to.

```js
const myOnMouseDown = event => console.log('mouse down on', event.target);

<Draggable draggableId="draggable-1" index={0}>
  {(provided, snapshot) => {
    const onMouseDown = (() => {
      // dragHandleProps might be null
      if (!provided.dragHandleProps) {
        return onMouseDown;
      }

      // creating a new onMouseDown function that calls myOnMouseDown as well as the drag handle one.
      return (event) => {
        provided.dragHandleProps.onMouseDown(event);
        myOnMouseDown(event);
      };
    })();

    return (
      <div>
        <div
          ref={provided.innerRef}
          {...provided.draggableProps}
          {...provided.dragHandleProps}
          onMouseDown={onMouseDown}
        >
          Drag me!
        </div>
        {provided.placeholder}
      </div>
    );
  }}
</Draggable>;
```

- `provided.placeholder (?ReactElement)` The `Draggable` element has `position: fixed` applied to it while it is dragging. The role of the `placeholder` is to sit in the place that the `Draggable` was during a drag. It is needed to stop the `Droppable` list from collapsing when you drag. It is advised to render it as a sibling to the `Draggable` node. This is unlike `Droppable` where the `placeholder` needs to be *within* the `Droppable` node. When the library moves to `React` 16 the `placeholder` will be removed from api.

##### `placeholder` example

```js
<Draggable draggableId="draggable-1" index={0}>
  {(provided, snapshot) => (
    <div>
      <div ref={provided.innerRef} {...provided.draggableProps}>
        Drag me!
      </div>
      {/* Always render me - I will be null if not required */}
      {provided.placeholder}
    </div>
  )}
</Draggable>;
```

#### 2. Snapshot: (DraggableStateSnapshot)**

```js
type DraggableStateSnapshot = {|
  isDragging: boolean,
  // What Droppable (if any) the Draggable is currently over
  draggingOver: ?DroppableId,
|};
```

The `children` function is also provided with a small amount of state relating to the current drag state. This can be optionally used to enhance your component. A common use case is changing the appearance of a `Draggable` while it is being dragged. Note: if you want to change the cursor to something like `grab` you will need to add the style to the draggable. (See [Extending `DraggableProps.style`](#extending-draggableprops-style) above)

```js
<Draggable draggableId="draggable-1" index={0}>
  {(provided, snapshot) => {
    const style = {
      backgroundColor: snapshot.isDragging ? 'blue' : 'grey',
      ...provided.draggableProps.style,
    };

    return (
      <div>
        <div
          ref={provided.innerRef}
          {...provided.draggableProps}
          {...provided.dragHandleProps}
          style={style}
        >
          Drag me!
        </div>
        {provided.placeholder}
      </div>
    );
  }}
</Draggable>;
```

### Adding an `onClick` handler to a `Draggable` or a *drag handle*

You are welcome to add your own `onClick` handler to a `Draggable` or a *drag handle* (which might be the same element). `onClick` events handlers will always be called if a click occurred. If we are preventing the click then we the `event.defaultPrevented` property will be set to `true`. We prevent click events from occurring when the user was dragging an item. See [#sloppy-clicks-and-click-prevention-](sloppy clicks and click prevention) for more information.

### Interactive child elements within a `Draggable`

It is possible for your `Draggable` to contain interactive elements. By default we block dragging on these elements. By doing this we allow those elements to function in the usual way. Here is the list of interactive elements that we block dragging from by default:

- `input`
- `button`
- `textarea`
- `select`
- `option`
- `optgroup`
- `video`
- `audio`
- [`contenteditable`](https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes/contenteditable) (any elements that are `contenteditable` or are within a `contenteditable` container)

You can opt out of this behavior by adding the `disableInteractiveElementBlocking` prop to a `Draggable`. However, it is questionable as to whether you should be doing so because it will render the interactive element unusable. If you need to *conditionally* block dragging from interactive elements you can add the `disableInteractiveElementBlocking` prop to opt out of the default blocking and monkey patch the `dragHandleProps (DragHandleProps)` event handlers to disable dragging as required.

## `resetServerContext`

The `resetServerContext` function should be used when server side rendering (SSR). It ensures context state does not persist across multiple renders on the server which would result in client/server markup mismatches after multiple requests are rendered on the server.

Use it before calling the server side render method:

```js
import { resetServerContext } from 'react-beautiful-dnd';
import { renderToString } from 'react-dom/server';

...

resetServerContext();
renderToString(...);
```

## Flow usage

`react-beautiful-dnd` is typed using [`flowtype`](https://flow.org). This greatly improves internal consistency within the codebase. We also expose a number of public types which will allow you to type your javascript if you would like to. If you are not using `flowtype` this will not inhibit you from using the library. It is just extra safety for those who want it.

### Public flow types

```js
// id's
type Id = string;
type TypeId = Id;
type DroppableId = Id;
type DraggableId = Id;

// hooks
type DragStart = {|
  draggableId: DraggableId,
  type: TypeId,
  source: DraggableLocation,
|}

type DragUpdate = {|
  ...DragStart,
  // may not have any destination (drag to nowhere)
  destination: ?DraggableLocation,
|}

type DropResult = {|
  ...DragUpdate,
  reason: DropReason,
|}

type DropReason = 'DROP' | 'CANCEL'

type DraggableLocation = {|
  droppableId: DroppableId,
  // the position of the droppable within a droppable
  index: number
|};

// Droppable
type DroppableProvided = {|
  innerRef: (?HTMLElement) => void,
  placeholder: ?ReactElement,
|}

type DroppableStateSnapshot = {|
  isDraggingO