Using the Popover API
=====================

The **Popover API** provides developers with a standard, consistent, flexible mechanism for displaying popover content on top of other page content. Popover content can be controlled either declaratively using HTML attributes, or via JavaScript. This article provides a detailed guide to using all of its features.

Creating declarative popovers
-----------------------------

In its simplest form, a popover is created by adding the `popover` attribute to the element that you want to contain your popover content. An `id` is also needed to associate the popover with its controls.


```html
<div id="mypopover" popover>Popover content</div>
```


**Note:** Setting the `popover` attribute with no value is equivalent to setting `popover="auto"`.

Adding this attribute causes the element to be hidden on page load by having `display: none` set on it. To show/hide the popover, you need to add some control buttons. You can set a `<button>` (or `<input>` of `type="button"`) as a popover control button by giving it a `popovertarget` attribute, the value of which should be the ID of the popover to control:


```html
<button popovertarget="mypopover">Toggle the popover</button>
<div id="mypopover" popover>Popover content</div>
```


The default behavior is for the button to be a toggle button — pressing it repeatedly will toggle the popover between showing and hidden.

If you want to change that behavior, you can use the `popovertargetaction` attribute — this takes a value of `"hide"`, `"show"`, or `"toggle"`. For example, to create separate show and hide buttons, you could do this:


```html
<button popovertarget="mypopover" popovertargetaction="show">
  Show popover
</button>
<button popovertarget="mypopover" popovertargetaction="hide">
  Hide popover
</button>
<div id="mypopover" popover>Popover content</div>
```


You can see how the previous code snippet renders in our Basic declarative popover example (source).

**Note:** If the `popovertargetaction` attribute is omitted, `"toggle"` is the default action that will be performed by a control button.

When a popover is shown, it has `display: none` removed from it and it is put into the top layer so it will sit on top of all other page content.

auto state, and "light dismiss"
-------------------------------

When a popover element is set with `popover` or `popover="auto"` as shown above, it is said to have **auto state**. The two important behaviors to note about auto state are:

* The popover can be "light dismissed" — this means that you can hide the popover by clicking outside it.
* The popover can also be closed, using browser-specific mechanisms such as pressing the `Esc` key.
* Usually, only one popover can be shown at a time — showing a second popover when one is already shown will hide the first one. The exception to this rule is when you have nested auto popovers. See the Nested popovers section for more details.

**Note:** `popover="auto"` popovers are also dismissed by successful `HTMLDialogElement.showModal()` and `Element.requestFullscreen()` calls on other elements in the document. Bear in mind however that calling these methods on a shown popover will result in failure because those behaviors don't make sense on an already-shown popover. You can however call them on an element with the `popover` attribute that isn't currently being shown.

Auto state is useful when you only want to show a single popover at once. Perhaps you have multiple teaching UI messages that you want to show, but don't want the display to start getting cluttered and confusing, or perhaps you are showing status messages where the new status overrides any previous status.

You can see the behavior described above in action in our Multiple auto popovers example (source). Try light dismissing the popovers after they are shown, and see what happens when you try to show both at the same time.

Using manual popover state
--------------------------

The alternative to auto state is **manual state**, achieved by setting `popover="manual"` on your popover element:


```html
<div id="mypopover" popover="manual">Popover content</div>
```


In this state:

* The popover cannot be "light dismissed", although declarative show/hide/toggle buttons (as seen earlier) will still work.
* Multiple independent popovers can be shown at a time.

You can see this behavior in action in our Multiple manual popovers example (source).

Showing popovers via JavaScript
-------------------------------

You can also control popovers using a JavaScript API.

The `HTMLElement.popover` property can be used to get or set the `popover` attribute. This can be used to create a popover via JavaScript, and is also useful for feature detection. For example:


```js
function supportsPopover() {
  return HTMLElement.prototype.hasOwnProperty("popover");
}
```


Similarly:

* `HTMLButtonElement.popoverTargetElement` and `HTMLInputElement.popoverTargetElement` provide an equivalent to the `popovertarget` attribute, allowing you to set up the control button(s) for a popover, although the property value taken is a reference to the popover DOM element to control.
* `HTMLButtonElement.popoverTargetAction` and `HTMLInputElement.popoverTargetAction` provide an equivalent to the `popovertargetaction` global HTML attribute, allowing you to specify the action taken by a control button.

Putting these three together, you can programmatically set up a popover and its control button, like so:


```js
const popover = document.getElementById("mypopover");
const toggleBtn = document.getElementById("toggleBtn");

const keyboardHelpPara = document.getElementById("keyboard-help-para");

const popoverSupported = supportsPopover();

if (popoverSupported) {
  popover.popover = "auto";
  toggleBtn.popoverTargetElement = popover;
  toggleBtn.popoverTargetAction = "toggle";
} else {
  toggleBtn.style.display = "none";
}
```


You also have several methods to control showing and hiding:

* `HTMLElement.showPopover()` to show a popover.
* `HTMLElement.hidePopover()` to hide a popover.
* `HTMLElement.togglePopover()` to toggle a popover.

For example, you might want to provide the ability to toggle a help popover on and off by clicking a button or pressing a particular key on the keyboard. The first one could be achieved declaratively, or you could do it using JavaScript as shown above.

For the second one, you could create an event handler that programs two separate keys — one to open the popover and one to close it again:


```js
document.addEventListener("keydown", (event) => {
  if (event.key === "h") {
    if (popover.matches(":popover-open")) {
      popover.hidePopover();
    }
  }

  if (event.key === "s") {
    if (!popover.matches(":popover-open")) {
      popover.showPopover();
    }
  }
});
```


This example uses `Element.matches()` to programmatically check whether a popover is currently showing. The `:popover-open` pseudo-class matches only popovers that are currently being shown. This is important to avoid the errors that are thrown if you try to show an already-shown popover, or hide an already-hidden popover.

Alternatively, you could program a single key to show *and* hide the popover like this:


```js
document.addEventListener("keydown", (event) => {
  if (event.key === "h") {
    popover.togglePopover();
  }
});
```


See our Toggle help UI example (source) to see the popover JavaScript properties, feature detection, and `togglePopover()` method in action.

Dismissing popovers automatically via a timer
---------------------------------------------

Another common pattern in JavaScript is dismissing popovers automatically after a certain amount of time. You might for example want to create a system of "toast" notifications, where you have multiple actions underway at a time (for example multiple files uploading), and want to show a notification when each one succeeds or fails. For this you'll want to use manual popovers so you can show several at the same time, and use `setTimeout()` to remove them. A function for handling such popovers might look like so:


```js
function makeToast(result) {
  const popover = document.createElement("article");
  popover.popover = "manual";
  popover.classList.add("toast");
  popover.classList.add("newest");

  let msg;

  if (result === "success") {
    msg = "Action was successful!";
    popover.classList.add("success");
    successCount++;
  } else if (result === "failure") {
    msg = "Action failed!";
    popover.classList.add("failure");
    failCount++;
  } else {
    return;
  }

  popover.textContent = msg;
  document.body.appendChild(popover);
  popover.showPopover();

  updateCounter();

  setTimeout(() => {
    popover.hidePopover();
    popover.remove();
  }, 4000);
}
```


You can also use the `beforetoggle` event to perform a follow-up action when a popover shows or hides. In our example we execute a `moveToastsUp()` function to make the toasts all move up the screen to make way each time a new toast appears:


```js
popover.addEventListener("toggle", (event) => {
  if (event.newState === "open") {
    moveToastsUp();
  }
});

function moveToastsUp() {
  const toasts = document.querySelectorAll(".toast");

  toasts.forEach((toast) => {
    if (toast.classList.contains("newest")) {
      toast.style.bottom = `5px`;
      toast.classList.remove("newest");
    } else {
      const prevValue = toast.style.bottom.replace("px", "");
      const newValue = parseInt(prevValue) + 50;
      toast.style.bottom = `${newValue}px`;
    }
  });
}
```


See our Toast popover example (source) to see the above example snippets in action, and full comments for explanation.

Nested popovers
---------------

There is an exception to the rule about not displaying multiple auto popovers at once — when they are nested inside one another. In such cases, multiple popovers are allowed to both be open at the same time, due to their relationship with each other. This pattern is supported to enable use cases such as nested popover menus.

There are three different ways to create nested popovers:

1. Direct DOM descendants:

```html
<div popover>
  Parent
  <div popover>Child</div>
</div>
```

2. Via invoking/control elements:

```html
<div popover>
  Parent
  <button popovertarget="foo">Click me</button>
</div>

<div popover id="foo">Child</div>
```

3. Via the `anchor` attribute:

```html
<div popover id="foo">Parent</div>

<div popover anchor="foo">Child</div>
```


See our Nested popover menu example (source) for an example. You'll notice that quite a few event handlers have been used to display and hide the subpopover appropriately during mouse and keyboard access, and also to hide both menus when an option is selected from either. Depending on how you handle loading of new content , either in an SPA or multi-page website, some of all of these may not be necessary, but they have been included in this demo for illustrative purposes.

Styling popovers
----------------

The popover API has some related CSS features available that are worth looking at.

In terms of styling the actual popover, you can select all popovers with a simple attribute selector (`[popover]`), or you select popovers that are showing using a new pseudo-class — `:popover-open`.

When looking at the first couple of examples linked at the start of the article, you may have noticed that the popovers appear in the middle of the viewport. This is the default styling, achieved like this in the UA stylesheet:


```css
[popover] {
  position: fixed;
  inset: 0;
  width: fit-content;
  height: fit-content;
  margin: auto;
  border: solid;
  padding: 0.25em;
  overflow: auto;
  color: CanvasText;
  background-color: Canvas;
}
```


To override the default styles and get the popover to appear somewhere else on your viewport, you would need to override the above styles with something like this:


```css
:popover-open {
  width: 200px;
  height: 100px;
  position: absolute;
  inset: unset;
  bottom: 5px;
  right: 5px;
  margin: 0;
}
```


You can see an isolated example of this in our Popover positioning example (source).

The `::backdrop` pseudo-element is a full-screen element placed directly behind showing popover elements in the top layer, allowing effects to be added to the page content behind the popover(s) if desired. You might for example want to blur out the content behind the popover to help focus the user's attention on it:


```css
::backdrop {
  backdrop-filter: blur(3px);
}
```


See our Popover blur background example (source) for an idea of how this renders.

Animating popovers
------------------

Popovers are set to `display: none;` when hidden and `display: block;` when shown, as well as being removed from / added to the top layer and the accessibility tree. Therefore, for popovers to be animated, the `display` property needs to be animatable. Supporting browsers animate `display` with a variation on the discrete animation type. Specifically, the browser will flip between `none` and another value of `display` so that the animated content is shown for the entire animation duration. So, for example:

* When animating `display` from `none` to `block` (or another visible `display` value), the value will flip to `block` at `0%` of the animation duration so it is visible throughout.
* When animating `display` from `block` (or another visible `display` value) to `none`, the value will flip to `none` at `100%` of the animation duration so it is visible throughout.

**Note:** When animating using CSS transitions, `transition-behavior: allow-discrete` needs to be set to enable the above behavior. When animating with CSS animations, the above behavior is available by default; an equivalent step is not required.

### Transitioning a popover

When animating popovers with CSS transitions, the following features are required:

`@starting-style` at-rule

Provides a set of starting values for properties set on the popover that you want to transition from when it is first shown. This is needed to avoid unexpected behavior. By default, CSS transitions only occur when a property changes from one value to another on a visible element; they are not triggered on an element's first style update, or when the `display` type changes from `none` to another type.

`display` property

Add `display` to the transitions list so that the popover will remain as `display: block` (or another visible `display` value) for the duration of the transition, ensuring the other transitions are visible.

`overlay` property

Include `overlay` in the transitions list to ensure the removal of the popover from the top layer is deferred until the transition completes, again ensuring the transition is visible.

`transition-behavior` property

Set `transition-behavior: allow-discrete` on the `display` and `overlay` transitions (or on the `transition` shorthand) to enable discrete transitions on these two properties that are not by default animatable.

Let's have a look at an example so you can see what this looks like:

#### HTML

The HTML contains a `<div>` element declared to be a popover via the global `popover` HTML attribute, and a `<button>` element designated as the popover's display control:


```html
<button popovertarget="mypopover">Show the popover</button>
<div popover="auto" id="mypopover">I'm a Popover! I should animate.</div>
```


#### CSS

The two popover properties we want to transition are `opacity` and `transform`. We want the popover to fade in or out while growing or shrinking horizontally. To achieve this, we set a starting state for these properties on the hidden state of the popover element (selected with the `[popover]` attribute selector) and an end state for the shown state of the popover (selected via the `:popover-open` pseudo-class). We also use the `transition` property to define the properties to animate and the animation's duration as the popover gets shown or hidden.


```css
html {
  font-family: Arial, Helvetica, sans-serif;
}

/\* Transition for the popover itself \*/

[popover]:popover-open {
  opacity: 1;
  transform: scaleX(1);
}

[popover] {
  font-size: 1.2rem;
  padding: 10px;

  /\* Final state of the exit animation \*/
  opacity: 0;
  transform: scaleX(0);

  transition:
    opacity 0.7s,
    transform 0.7s,
    overlay 0.7s allow-discrete,
    display 0.7s allow-discrete;
  /\* Equivalent to
 transition: all 0.7s allow-discrete; \*/
}

/\* Needs to be after the previous [popover]:popover-open rule
to take effect, as the specificity is the same \*/
@starting-style {
  [popover]:popover-open {
    opacity: 0;
    transform: scaleX(0);
  }
}

/\* Transition for the popover's backdrop \*/

[popover]::backdrop {
  background-color: rgb(0 0 0 / 0%);
  transition:
    display 0.7s allow-discrete,
    overlay 0.7s allow-discrete,
    background-color 0.7s;
  /\* Equivalent to
 transition: all 0.7s allow-discrete; \*/
}

[popover]:popover-open::backdrop {
  background-color: rgb(0 0 0 / 25%);
}

/\* The nesting selector (&) cannot represent pseudo-elements
so this starting-style rule cannot be nested \*/

@starting-style {
  [popover]:popover-open::backdrop {
    background-color: rgb(0 0 0 / 0%);
  }
}
```


As discussed earlier, we have also:

* Set a starting state for the `transition` inside the `@starting-style` block.
* Added `display` to the list of transitioned properties so that the animated element is visible (set to `display: block`) throughout the popover's entry and exit animations. Without this, the exit animation would not be visible; in effect, the popover would just disappear.
* Added `overlay` to the list of transitioned properties to make sure that the removal of the element from the top layer is deferred until the animation has been completed. The effect of this may not be noticeable for basic animations such as this one, but in more complex cases, omitting this property can result in the element being removed from the overlay before the transition completes.
* Set `allow-discrete` on both properties in the above transitions to enable discrete transitions.

You'll note that we've also included a transition on the `::backdrop` appearing behind the popover when it opens, providing a nice darkening animation.

#### Result

The code renders as follows:

**Note:** Because popovers change from `display: none` to `display: block` each time they are shown, the popover transitions from its `@starting-style` styles to its `[popover]:popover-open` styles every time the entry transition occurs. When the popover closes, it transitions from its `[popover]:popover-open` state to the default `[popover]` state.

It is possible for the style transition on entry and exit to be different in such cases. See our Demonstration of when starting styles are used example for a proof of this.

### A popover keyframe animation

When animating a popover with CSS keyframe animations, there are some differences to note:

* You don't provide a `@starting-style`; you include your "to" and "from" `display` values in keyframes.
* You don't explicitly enable discrete animations; there is no equivalent to `allow-discrete` inside keyframes.
* You don't need to set `overlay` inside keyframes either; the `display` animation handles the animation of the popover from shown to hidden.

Let's look at an example.

#### HTML

The HTML contains a `<div>` element declared as a popover, and a `<button>` element designated as the popover's display control:


```html
<button popovertarget="mypopover">Show the popover</button>
<div popover="auto" id="mypopover">I'm a Popover! I should animate.</div>
```


#### CSS

We have defined keyframes that specify the desired entry and exit animations, and an entry animation for the backdrop only. Note that it wasn't possible to animate the backdrop fade out — the backdrop is immediately removed from the DOM when the popover is closed, so there is nothing to animate.


```css
html {
  font-family: Arial, Helvetica, sans-serif;
}

[popover] {
  font-size: 1.2rem;
  padding: 10px;
  animation: fade-out 0.7s ease-out;
}

[popover]:popover-open {
  animation: fade-in 0.7s ease-out;
}

[popover]:popover-open::backdrop {
  animation: backdrop-fade-in 0.7s ease-out forwards;
}

/\* Animation keyframes \*/

@keyframes fade-in {
  0% {
    opacity: 0;
    transform: scaleX(0);
  }

  100% {
    opacity: 1;
    transform: scaleX(1);
  }
}

@keyframes fade-out {
  0% {
    opacity: 1;
    transform: scaleX(1);
    /\* display needed on the closing animation to keep the popover
 visible until the animation ends \*/
    display: block;
  }

  100% {
    opacity: 0;
    transform: scaleX(0);
    /\* display: none not required here because it is the default value
 for a closed popover, but including it so the behavior is clear \*/
    display: none;
  }
}

@keyframes backdrop-fade-in {
  0% {
    background-color: rgb(0 0 0 / 0%);
  }

  100% {
    background-color: rgb(0 0 0 / 25%);
  }
}
```


#### Result

The code renders as follows: