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XMLHttpRequest: getAllResponseHeaders() method

The XMLHttpRequest method getAllResponseHeaders() returns all the response headers, separated by CRLF, as a string, or returns null if no response has been received.

If a network error happened, an empty string is returned.

Note: For multipart requests, this returns the headers from the current part of the request, not from the original channel.

Syntax

getAllResponseHeaders()

Parameters

None.

Return value

A string representing all of the response's headers (except those whose field name is Set-Cookie) separated by CRLF, or null if no response has been received. If a network error happened, an empty string is returned.

An example of what a raw header string looks like:

http

date: Fri, 08 Dec 2017 21:04:30 GMT\r\n
content-encoding: gzip\r\n
x-content-type-options: nosniff\r\n
server: meinheld/0.6.1\r\n
x-frame-options: DENY\r\n
content-type: text/html; charset=utf-8\r\n
connection: keep-alive\r\n
strict-transport-security: max-age=63072000\r\n
vary: Cookie, Accept-Encoding\r\n
content-length: 6502\r\n
x-xss-protection: 1; mode=block\r\n

Each line is terminated by both carriage return and line feed characters (\r\n). These are essentially delimiters separating each of the headers.

Note: In modern browsers, the header names are returned in all lower case, as per the latest spec.

Examples

This example examines the headers in the request's readystatechange event. The code shows how to obtain the raw header string, as well as how to convert it into an array of individual headers and then how to take that array and create a mapping of header names to their values.

const request = new XMLHttpRequest();
request.open("GET", "foo.txt", true);
request.send();

request.onreadystatechange = () => {
  if (request.readyState === this.HEADERS_RECEIVED) {
    // Get the raw header string
    const headers = request.getAllResponseHeaders();

    // Convert the header string into an array
    // of individual headers
    const arr = headers.trim().split(/[\r\n]+/);

    // Create a map of header names to values
    const headerMap = {};
    arr.forEach((line) => {
      const parts = line.split(": ");
      const header = parts.shift();
      const value = parts.join(": ");
      headerMap[header] = value;
    });
  }
};

Once this is done, you can, for example:

const contentType = headerMap["content-type"];

This obtains the value of the Content-Type header into the variable contentType.

Specifications

Specification
XMLHttpRequest Standard # the-getallresponseheaders()-method

Browser compatibility