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.

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.

A boolean value.

Creating an empty Headers object is simple:

const 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

• ServiceWorker API
• HTTP access control (CORS)
• HTTP