Headers.set()

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.get('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

Update compatibility data on GitHub
DesktopMobile
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidEdge MobileFirefox for AndroidOpera for AndroidSafari on iOSSamsung Internet
Basic support
Experimental
Chrome Full support 42
Full support 42
Full support 41
Disabled
Disabled From version 41: this feature is behind the Experimental Web Platform Features preference. To change preferences in Chrome, visit chrome://flags.
Edge Full support YesFirefox Full support 39
Full support 39
Full support 34
Disabled
Disabled From version 34: this feature is behind the dom.fetch.enabled preference. To change preferences in Firefox, visit about:config.
IE No support NoOpera Full support 29
Full support 29
Full support 28
Disabled
Disabled From version 28: this feature is behind the Experimental Web Platform Features preference.
Safari No support NoWebView Android Full support 42
Full support 42
Full support 41
Disabled
Disabled From version 41: this feature is behind the Experimental Web Platform Features preference.
Chrome Android Full support 42
Full support 42
Full support 41
Disabled
Disabled From version 41: this feature is behind the Experimental Web Platform Features preference. To change preferences in Chrome, visit chrome://flags.
Edge Mobile Full support YesFirefox Android No support NoOpera Android Full support 29
Full support 29
Full support 28
Disabled
Disabled From version 28: this feature is behind the Experimental Web Platform Features preference.
Safari iOS No support NoSamsung Internet Android Full support 4.0

Legend

Full support  
Full support
No support  
No support
Experimental. Expect behavior to change in the future.
Experimental. Expect behavior to change in the future.
User must explicitly enable this feature.
User must explicitly enable this feature.

See also

Document Tags and Contributors

Contributors to this page: mfluehr, fscholz, Rob W, chrisdavidmills, erikadoyle, jpmedley, kscarfone
Last updated by: mfluehr,