Headers: has() method

{{APIRef("Fetch API")}} {{AvailableInWorkers}}

The has() method of the {{domxref("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 {{Glossary("Forbidden_request_header", "forbidden request headers")}} and {{Glossary("Forbidden_response_header_name", "forbidden response header names")}}.

Syntax

has(name)

Parameters

• 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 {{jsxref("TypeError")}}.

Return value

A boolean value.

Examples

Creating an empty Headers object is simple:

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

You could add a header to this using {{domxref("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

Specifications

{{Specifications}}

Browser compatibility

{{Compat}}

See also

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