Headers()
The Headers()
constructor creates a new
Headers
object.
Syntax
new Headers()
new Headers(init)
Parameters
init
Optional-
An object containing any HTTP headers that you want to pre-populate your
Headers
object with. This can be a simple object literal withString
values, an array of name-value pairs, where each pair is a 2-element string array; or an existingHeaders
object. In the last case, the newHeaders
object copies its data from the existingHeaders
object.
Examples
Creating an empty Headers
object is simple:
const myHeaders = new Headers(); // Currently empty
You could add a header to this using Headers.append
:
myHeaders.append('Content-Type', 'image/jpeg');
myHeaders.get('Content-Type'); // Returns 'image/jpeg'
Or you can add the headers you want as the Headers
object is created. In
the following snippet we create a new Headers
object, adding some headers
by passing the constructor an init object as an argument:
const httpHeaders = { 'Content-Type' : 'image/jpeg', 'X-My-Custom-Header' : 'Zeke are cool' };
const myHeaders = new Headers(httpHeaders);
You can now create another Headers
object, passing it the first
Headers
object as its init object:
const secondHeadersObj = new Headers(myHeaders);
secondHeadersObj.get('Content-Type'); // Would return 'image/jpeg' — it inherits it from the first headers object
You can also add the headers you want as the Headers
object is created by using a two-dimensional array to add multiple headers with the same values. In
the following snippet we create a new Headers
object with multiple Set-Cookie
headers
by passing the constructor an init array as an argument:
const headers = [
['Set-Cookie', 'greeting=hello'],
['Set-Cookie', 'name=world']
];
const myHeaders = new Headers(headers);
Specifications
Specification |
---|
Fetch Standard # ref-for-dom-headers① |
Browser compatibility
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