XMLHttpRequest

XMLHttpRequest (XHR) objects are used to interact with servers. You can retrieve data from a URL without having to do a full page refresh. This enables a Web page to update just part of a page without disrupting what the user is doing.

XMLHttpRequest is used heavily in AJAX programming.

Despite its name, XMLHttpRequest can be used to retrieve any type of data, not just XML.

If your communication needs to involve receiving event data or message data from a server, consider using server-sent events through the EventSource interface. For full-duplex communication, WebSockets may be a better choice.

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

Constructor

XMLHttpRequest(): The constructor initializes an XMLHttpRequest. It must be called before any other method calls.

Properties

This interface also inherits properties of XMLHttpRequestEventTarget and of EventTarget.

XMLHttpRequest.readyState Read only: Returns an unsigned short, the state of the request.
XMLHttpRequest.response Read only: Returns an ArrayBuffer, Blob, Document, JavaScript object, or a DOMString, depending on the value of XMLHttpRequest.responseType, that contains the response entity body.
XMLHttpRequest.responseText Read only: Returns a DOMString that contains the response to the request as text, or null if the request was unsuccessful or has not yet been sent.
XMLHttpRequest.responseType: Is an enumerated value that defines the response type.
XMLHttpRequest.responseURL Read only: Returns the serialized URL of the response or the empty string if the URL is null.
XMLHttpRequest.responseXML Read only: Returns a Document containing the response to the request, or null if the request was unsuccessful, has not yet been sent, or cannot be parsed as XML or HTML. Not available in workers.
XMLHttpRequest.status Read only: Returns an unsigned short with the status of the response of the request.
XMLHttpRequest.statusText Read only: Returns a DOMString containing the response string returned by the HTTP server. Unlike XMLHttpRequest.status, this includes the entire text of the response message ("200 OK", for example).

Note: According to the HTTP/2 specification (8.1.2.4 Response Pseudo-Header Fields), HTTP/2 does not define a way to carry the version or reason phrase that is included in an HTTP/1.1 status line.
XMLHttpRequest.timeout: Is an unsigned long representing the number of milliseconds a request can take before automatically being terminated.
XMLHttpRequest.upload Read only: Is an XMLHttpRequestUpload, representing the upload process.
XMLHttpRequest.withCredentials: Is a boolean value that indicates whether or not cross-site Access-Control requests should be made using credentials such as cookies or authorization headers.

Non-standard properties

XMLHttpRequest.channelRead only: The channel used by the object when performing the request.
XMLHttpRequest.mozAnonRead only: Is a boolean. If true, the request will be sent without cookie and authentication headers.
XMLHttpRequest.mozSystemRead only: Is a boolean. If true, the same origin policy will not be enforced on the request.
XMLHttpRequest.mozBackgroundRequest: Is a boolean. It indicates whether or not the object represents a background service request.

Methods

XMLHttpRequest.abort(): Aborts the request if it has already been sent.
XMLHttpRequest.getAllResponseHeaders(): Returns all the response headers, separated by CRLF, as a string, or null if no response has been received.
XMLHttpRequest.getResponseHeader(): Returns the string containing the text of the specified header, or null if either the response has not yet been received or the header doesn't exist in the response.
XMLHttpRequest.open(): Initializes a request.
XMLHttpRequest.overrideMimeType(): Overrides the MIME type returned by the server.
XMLHttpRequest.send(): Sends the request. If the request is asynchronous (which is the default), this method returns as soon as the request is sent.
XMLHttpRequest.setRequestHeader(): Sets the value of an HTTP request header. You must call setRequestHeader()after open(), but before send().

Events

abort: Fired when a request has been aborted, for example because the program called XMLHttpRequest.abort(). Also available via the onabort event handler property.
error: Fired when the request encountered an error. Also available via the onerror event handler property.
load: Fired when an XMLHttpRequest transaction completes successfully. Also available via the onload event handler property.
loadend: Fired when a request has completed, whether successfully (after load) or unsuccessfully (after abort or error). Also available via the onloadend event handler property.
loadstart: Fired when a request has started to load data. Also available via the onloadstart event handler property.
progress: Fired periodically when a request receives more data. Also available via the onprogress event handler property.
readystatechange: Fired whenever the readyState property changes. Also available via the onreadystatechange event handler property.
timeout: Fired when progress is terminated due to preset time expiring. Also available via the ontimeout event handler property.

Specifications

Specification
XMLHttpRequest Standard # interface-xmlhttprequest

Browser compatibility

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