Headers
ΒΆ6.1 Headers Class of whatwg spec
The Headers interface of the Fetch API allows you to perform various actions on HTTP request and response headers. These actions include retrieving, setting, adding to, and removing. A Headers object has an associated header list, which is initially empty and consists of zero or more name and value pairs. You can add to this using methods like append() (see Examples.) In all methods of this interface, header names are matched by case-insensitive byte sequence.
For security reasons, some headers can only be controller by the user agent. These headers include the forbidden header names and forbidden response header names.
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.
Value members
Concrete methods
The append() method of the Headers interface appends a new value onto an existing header inside a Headers object, or adds the header if it does not already exist.
The append() method of the Headers interface appends a new value onto an existing header inside a Headers object, or adds the header if it does not already exist.
The difference between Headers.set and append() is that if the specified header already exists and accepts multiple values, Headers.set will overwrite the existing value with the new one, whereas append() will append the new value onto the end of the set of values.
The delete() method of the Headers interface deletes a header from the current Headers object.
The delete() method of the Headers interface deletes a header from the current Headers object.
The get() method of the Headers interface returns the first value of a given header from within a Headers object . If the requested header doesn't exist in the Headers object, the call returns null.
The get() method of the Headers interface returns the first value of a given header from within a Headers object . If the requested header doesn't exist in the Headers object, the call returns null.
- Value parameters:
- name
a ByteString, ie. only ASCII chars
The getAll() method of the Headers interface returns an array of all the values of a header within a Headers object with a given name. If the requested header doesn't exist in the Headers object, it returns an empty array.
The getAll() method of the Headers interface returns an array of all the values of a header within a Headers object with a given name. If the requested header doesn't exist in the Headers object, it returns an empty array.
- Value parameters:
- name
a ByteString, ie. only ASCII chars
The has() method of the Headers interface returns a boolean stating whether a Headers object contains a certain header.
The has() method of the Headers interface returns a boolean stating whether a Headers object contains a certain header.
- Value parameters:
- name
a ByteString, ie. only ASCII chars
The set() method of the Headers interface sets a new value for an existing header inside a Headers object, or adds the header if it does not already exist.
The set() method of the Headers interface sets a new value for an existing header inside a Headers object, or adds the header if it does not already exist.
The difference between set() and Headers.append is that if the specified header already exists and accepts multiple values, set() overwrites the existing value with the new one, whereas Headers.append appends the new value to the end of the set of values.
Not all headers can be set. See the list of forbidden header names in https://fetch.spec.whatwg.org/#terminology-headers