Headers.has() - Web APIs 编辑

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
Fetch The definition of 'has()' in that specification.	Living Standard

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