XMLHttpRequest API
==================

**Note:** This feature is available in Web Workers, except for Service Workers

The **XMLHttpRequest API** enables web apps to make HTTP requests to web servers and receive the responses programmatically using JavaScript. This in turn enables a website to update just part of a page with data from the server, rather than having to navigate to a whole new page. This practice is also sometimes known as Ajax.

The Fetch API is the more flexible and powerful replacement for the XMLHttpRequest API. The Fetch API uses promises instead of events to handle asynchronous responses, integrates well with service workers, and supports advanced aspects of HTTP such as CORS. For these reasons, the Fetch API is usually used in modern web apps instead of `XMLHttpRequest`.

Concepts and usage
------------------

The central interface in the XMLHttpRequest API is `XMLHttpRequest`. To make an HTTP request:

1. Create a new `XMLHttpRequest` instance by calling its constructor.
2. Initialize it by calling `XMLHttpRequest.open()`. At this point you provide the URL for the request, the HTTP method to use, and optionally, a username and password.
3. Attach event handlers to get the result of the request. For example, the `load` event is fired when the request has successfully completed, and the `error` event is fired in various error conditions.
4. Send the request by calling `XMLHttpRequest.send()`.

For an in-depth guide to the XMLHttpRequest API, see Using XMLHttpRequest.

Interfaces
----------

`FormData`

An object representing `<form>` fields and their values, which can be sent to a server using `XMLHttpRequest` or `fetch()`.

`ProgressEvent`

A subclass of `Event` which is passed into the `progress`, and which contains information about how much of the request has been completed.

`XMLHttpRequest`

Represents a single HTTP request.

`XMLHttpRequestEventTarget`

A superclass of both `XMLHttpRequest` and `XMLHttpRequestUpload`, defining the events that are available in both of those interfaces.

`XMLHttpRequestUpload`

Represents the upload process for an HTTP upload. Provides events enabling code to track the progress of an upload.

Examples
--------

### Fetching JSON data from the server

In this example we fetch a JSON file from https://raw.githubusercontent.com/, adding event listeners to show the progress of the event.

#### HTML


```html
<div class="controls">
  <button class="xhr" type="button">Click to start XHR</button>
</div>

<textarea readonly class="event-log"></textarea>
```


```
.event-log {
  width: 25rem;
  height: 5rem;
  border: 1px solid black;
  margin: 0.5rem;
  padding: 0.2rem;
}

button {
  width: 12rem;
  margin: 0.5rem;
}
```


#### JavaScript


```js
const xhrButton = document.querySelector(".xhr");
const log = document.querySelector(".event-log");
const url =
  "https://raw.githubusercontent.com/mdn/content/main/files/en-us/\_wikihistory.json";

function handleEvent(e) {
  log.textContent = `${log.textContent}${e.type}: ${e.loaded} bytes transferred\n`;
}

function addListeners(xhr) {
  xhr.addEventListener("loadstart", handleEvent);
  xhr.addEventListener("load", handleEvent);
  xhr.addEventListener("loadend", handleEvent);
  xhr.addEventListener("progress", handleEvent);
  xhr.addEventListener("error", handleEvent);
  xhr.addEventListener("abort", handleEvent);
}

xhrButton.addEventListener("click", () => {
  log.textContent = "";

  const xhr = new XMLHttpRequest();
  xhr.open("GET", url);
  addListeners(xhr);
  xhr.send();
});
```


#### Result

Specifications
--------------

| Specification |
| --- |
| XMLHttpRequest Standard  |

Browser compatibility
---------------------

BCD tables only load in the browser with JavaScript enabled. Enable JavaScript to view data.

See also
--------

* Fetch API