Headers

A Headers object also has an associated guard, which takes a value of immutable, request, request-no-cors, response, or none. This affects whether the set(), delete(), and append() methods will mutate the header. For more information see Guard.

You can retrieve a Headers object via the Request.headers and Response.headers properties, and create a new Headers object using the Headers.Headers() constructor.

An object implementing Headers can directly be used in a for...of structure, instead of entries(): for (var p of myHeaders) is equivalent to for (var p of myHeaders.entries()).

Constructor

Headers.Headers()

Creates a new Headers object.

Methods

Headers.append()

Appends a new value onto an existing header inside a Headers object, or adds the header if it does not already exist.

Headers.delete()

Deletes a header from a Headers object.

Headers.entries()

Returns an iterator allowing to go through all key/value pairs contained in this object.

Headers.forEach()

Executes a provided function once for each array element.

Headers.get()

Returns a ByteString sequence of all the values of a header within a Headers object with a given name.

Headers.has()

Returns a boolean stating whether a Headers object contains a certain header.

Headers.keys()

Returns an iterator allowing you to go through all keys of the key/value pairs contained in this object.

Headers.set()

Sets a new value for an existing header inside a Headers object, or adds the header if it does not already exist.

Headers.values()

Returns an iterator allowing you to go through all values of the key/value pairs contained in this object.

Obsolete methods

Headers.getAll()

Used to return an array of all the values of a header within a Headers object with a given name; this method has now been deleted from the spec, and Headers.get() now returns all values instead of just one.

Examples

In the following snippet, we create a new header using the Headers() constructor, add a new header to it using append(), then return that header value using get():

var myHeaders = new Headers();

myHeaders.append('Content-Type', 'text/xml');
myHeaders.get('Content-Type') // should return 'text/xml'

The same can be achieved by passing an array of arrays or an object literal to the constructor:

var myHeaders = new Headers({
    'Content-Type': 'text/xml'
});

// or, using an array of arrays:
myHeaders = new Headers([
    ['Content-Type', 'text/xml']
]);

myHeaders.get('Content-Type') // should return 'text/xml'

Specifications

Browser compatibility

See also

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