This is an experimental technology
Because this technology's specification has not stabilized, check the compatibility table for the proper prefixes to use 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 spec changes.
The set()
method of the Headers
interface sets a new value for an existing header inside a Headers
object, or adds the header if it does not already exist.
The difference between set()
and Headers.append
is that if the specified header already exists and accepts multiple values, set()
overwrites the existing value with the new one, whereas Headers.append
appends the new value to 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.set(name,value);
Parameters
- name
- The name of the HTTP header you want to set to a new value. If the given name is not the name of an HTTP header, this method throws a
TypeError
. - value
- The new value you want to set.
Returns
Void.
Example
Creating an empty Headers
object is simple:
var myHeaders = new Headers(); // Currently empty
You could add a header to this using Headers.append
, then set a new value for this header using set()
:
myHeaders.append('Content-Type', 'image/jpeg'); myHeaders.set('Content-Type', 'text/html');
If the specified header does not already exist, set()
will create it and set its value to the specified value. If the specified header does already exist and does accept multiple values, set()
will overwrite the existing value with the new one:
myHeaders.set('Accept-Encoding', 'deflate'); myHeaders.set('Accept-Encoding', 'gzip'); myHeaders.getAll('Accept-Encoding'); // Returns [ "gzip" ]
You'd need Headers.append
to append the new value onto the values, not overwrite it.
Specifications
Specification | Status | Comment |
---|---|---|
Fetch The definition of 'set()' 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 |
Not supported |
29 |
Not supported |
Feature | Android | Firefox Mobile (Gecko) | Firefox OS (Gecko) | IE Phone | Opera Mobile | Safari Mobile | Chrome for Android |
---|---|---|---|---|---|---|---|
Basic support | Not supported | Not supported | Not supported | Not supported | Not supported | Not supported | Not supported |