Headers.append()

This is an experimental technology
Because this technology's specification has not stabilized, check the compatibility table for usage in various browsers. Also note that the syntax and behavior of an experimental technology is subject to change in future versions of browsers as the specification changes.

The append() method of the Headers interface appends a new value onto an existing header inside a Headers object, or adds the header if it does not already exist.

The difference between Headers.set and append() is that if the specified header already exists and accepts multiple values, Headers.set will overwrite the existing value with the new one, whereas append() will append the new value onto the end of the set of values.

For security reasons, some headers can only be controller by the user agent. These headers include the forbidden header names  and forbidden response header names.

Syntax

myHeaders.append(name,value);

Parameters

name
The name of the HTTP header you want to add to the Headers object.
value
The value of the HTTP header you want to add.

Returns

Void.

Example

Creating an empty Headers object is simple:

var myHeaders = new Headers(); // Currently empty

You could add a header to this using append():

myHeaders.append('Content-Type', 'image/jpeg');
myHeaders.get('Content-Type'); // Returns 'image/jpeg'

If the specified header already exists, append() will change its value to the specified value. If the specified header already exists and accepts multiple values, append() will append the new value to the end of the value set:

myHeaders.append('Accept-Encoding', 'deflate');
myHeaders.append('Accept-Encoding', 'gzip');
myHeaders.getAll('Accept-Encoding'); // Returns [ "deflate", "gzip" ]

To overwrite the old value with a new one, use Headers.set.

Specifications

Specification Status Comment
Fetch
The definition of 'append()' in that specification.
Living Standard  

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
Basic support 42
41 behind pref
 
39 (39)
34 behind pref
No support

29
28 behind pref

No support
Feature Android Firefox Mobile (Gecko) Firefox OS (Gecko) IE Phone Opera Mobile Safari Mobile Chrome for Android
Basic support No support No support No support No support No support No support No support

See also

Document Tags and Contributors

 Contributors to this page: chrisdavidmills, jpmedley, kscarfone
 Last updated by: chrisdavidmills,