Headers: has() method
{{APIRef("Fetch API")}} {{AvailableInWorkers}}
The has() method of the {{domxref("Headers")}}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")}}headers
and {{Glossary("Forbidden_response_header_name", "forbidden response header names")}}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")}}TypeError.
- : 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
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")}}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}}