Web/API/Headers/has

The has() method of the Headers interface returns a boolean stating whether a Headers object contains a certain header.

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

Syntax

myHeaders.has(name);

name: The name of the HTTP header you want to test for. If the given name is not a valid HTTP header name, this method throws a TypeError.

Creating an empty Headers object is simple:

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

You could add a header to this using Headers.append, then test for the existence of it using has():

myHeaders.append('Content-Type', 'image/jpeg');
myHeaders.has('Content-Type'); // Returns true
myHeaders.has('Accept-Encoding'); // Returns false

Specification	Status	Comment
FetchThe definition of 'has()' in that specification.	Living Standard

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
`has` 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 14	Firefox 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 No	Opera 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 No	WebView Android Full support 42	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.	Firefox Android No support No	Opera 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 No	Samsung Internet Android Full support 4.0

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.