XMLHttpRequest 是一個提供客戶端與伺服器間交換資料功能的 API。它提供了一個簡單的方式來從 URL 擷取資料且不須刷新整個頁面,這使得網頁可以只更新其中的一部分而不中斷使用者的操作。XMLHttpRequest 被大量使用於 AJAX 應用。

XMLHttpRequest 最早為微軟所設計,後被 Mozilla、Apple 及 Google 採用。目前WHATWG 進行標準化。僅管名字用的是 XML 與 HTTP,XMLHttpRequest 其實可以用來接收任何類型的資料,並不限於 XML。同時它也支援 HTTP 以外的通訊協定(包括 fileftp)。


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


This interface also inherits properties of XMLHttpRequestEventTarget and of EventTarget.

An EventHandler that is called whenever the readyState attribute changes.
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.
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 Not available to workers
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.
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).

Per HTTP/2 specification ( 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.

Is an unsigned long representing the number of milliseconds a request can take before automatically being terminated.
Is an EventHandler that is called whenever the request times out.
XMLHttpRequest.upload Read only
Is an XMLHttpRequestUpload, representing the upload process.
Is a Boolean that indicates whether or not cross-site Access-Control requests should be made using credentials such as cookies or authorization headers.


XMLHttpRequest.channelRead only
Is a nsIChannel. 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.
Is a boolean. It indicates whether or not the object represents a background service request.
XMLHttpRequest.mozResponseArrayBuffer 已過時 Gecko 6 Read only
Is an ArrayBuffer. The response to the request, as a JavaScript typed array.
XMLHttpRequest.multipart已過時 Gecko 22
This Gecko-only feature, a boolean, was removed in Firefox/Gecko 22. Please use Server-Sent Events, Web Sockets, or responseText from progress events instead.


onreadystatechange as a property of the XMLHttpRequest instance is supported in all browsers.

Since then, a number of additional event handlers were implemented in various browsers (onload, onerror, onprogress, etc.). These are supported in Firefox. In particular, see nsIXMLHttpRequestEventTarget and Using XMLHttpRequest.

More recent browsers, including Firefox, also support listening to the XMLHttpRequest events via standard addEventListener APIs in addition to setting on* properties to a handler function.


Aborts the request if it has already been sent.
Returns all the response headers, separated by CRLF, as a string, or null if no response has been received.
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.
Initializes a request. This method is to be used from JavaScript code; to initialize a request from native code, use openRequest() instead.
Overrides the MIME type returned by the server.
Sends the request. If the request is asynchronous (which is the default), this method returns as soon as the request is sent.
Sets the value of an HTTP request header. You must call setRequestHeader()after open(), but before send().


Initializes the object for use from C++ code.
Warning: This method must not be called from JavaScript.
Initializes a request. This method is to be used from native code; to initialize a request from JavaScript code, use open() instead. See the documentation for open().
A variant of the send() method that sends binary data.


Specification Status Comment
XMLHttpRequest Living Standard Live standard, latest version


Feature Chrome Edge Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
Basic support (XHR1) 1 (Yes) 1.0 (1.7 or earlier) 7 (Yes) 1.2
send(ArrayBuffer) 9 (Yes) 9.0 (9.0) 10 11.60 ?
send(ArrayBufferView) 22 (Yes) 20.0 (20.0) ? ? ?
send(Blob) 7 (Yes) 3.6 (1.9.2) 10 12 ?
send(FormData) 6 (Yes) 4.0 (2.0) 10 12 ?
sendAsBinary(DOMString) No support[1] No support 2.0 (1.8.1) No support No support No support
response 10 (Yes) 6.0 (6.0) 10 11.60 (Yes)
responseType = 'arraybuffer' 10 (Yes) 6.0 (6.0) 10 11.60 (Yes)
responseType = 'blob' 19 (Yes) 6.0 (6.0) 10 12 (Yes)
responseType = 'document' 18 (Yes) 11.0 (11.0) 10 No support 6.1
responseType = 'json' 31 No support 10.0 (10.0) No support 12[2]
No support 16
Progress Events 7 (Yes) 3.5 (1.9.1) 10 12 (Yes)
withCredentials 3 (Yes) 3.5 (1.9.1) 10 12 4
timeout 29.0 (Yes) 12.0 (12.0) 8 12
responseType = 'moz-blob' No support No support 12.0 (12.0) No support No support No support
Feature Android Chrome for Android Edge Firefox Mobile (Gecko) IE Phone Opera Mobile Safari Mobile
Basic support ? 1.0 (Yes) (Yes) ? ? ?
send(ArrayBuffer) ? ? (Yes) ? ? ? ?
send(ArrayBufferView) ? ? (Yes) ? ? ? ?
send(Blob) ? ? (Yes) ? ? ? ?
send(FormData) ? ? (Yes) ? ? ? ?
sendAsBinary(DOMString) ? ? No support ? ? ? ?
response ? ? (Yes) ? ? ? ?
responseType = 'arraybuffer' ? ? (Yes) ? ? ? ?
responseType = 'blob' ? ? (Yes) ? ? ? ?
responseType = 'document' ? ? (Yes) ? ? ? ?
responseType = 'json' ? ? No support ? ? ? ?
Progress Events ? ? (Yes) ? ? ? ?
withCredentials ? ? (Yes) ? ? ? ?
timeout ? ? (Yes) ? ? ? ?
responseType = 'moz-blob' ? ? No support ? ? ? ?

[1] There is a polyfill available to support sendAsBinary().

[2] Before switching to Blink/Chromium, Opera supported responseType=json between Opera 12 and Opera 15. Support was added again in Opera 17.



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