HTML in XMLHttpRequest

The W3C XMLHttpRequest specification adds HTML parsing support to XMLHttpRequest, which originally supported only XML parsing. This feature allows Web apps to obtain an HTML resource as a parsed DOM using XMLHttpRequest.

To get an overview of how to use XMLHttpRequest in general, see Using XMLHttpRequest.

Limitations

To discourage the synchronous use of XMLHttpRequest, HTML support is not available in the synchronous mode. Also, HTML support is only available if the responseType property has been set to "document". This limitation avoids wasting time parsing HTML uselessly when legacy code uses XMLHttpRequest in the default mode to retrieve responseText for text/html resources. Also, this limitation avoids problems with legacy code that assumes that responseXML is null for HTTP error pages (which often have a text/html response body).

Usage

Retrieving an HTML resource as a DOM using XMLHttpRequest works just like retrieving an XML resource as a DOM using XMLHttpRequest, except you can't use the synchronous mode and you have to explicitly request a document by assigning the string "document" to the responseType property of the XMLHttpRequest object after calling open() but before calling send().

const xhr = new XMLHttpRequest();
xhr.onload = () => {
  console.log(xhr.responseXML.title);
};
xhr.open("GET", "file.html");
xhr.responseType = "document";
xhr.send();

Character encoding

If the character encoding is declared in the HTTP Content-Type header, that character encoding is used. Failing that, if there is a byte order mark, the encoding indicated by the byte order mark is used. Failing that, if there is a <meta> element that declares the encoding within the first 1024 bytes of the file, that encoding is used. Otherwise, the file is decoded as UTF-8.

Specifications

Browser compatibility

See also

• XMLHttpRequest
• Using XMLHttpRequest