Headers: set() method
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.
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.
Syntax
js
set(name, value)
Parameters
name-
The name of the HTTP header you want to set to a new value. If the given name is not the name of an HTTP header, this method throws a
TypeError. value-
The new value you want to set.
Return value
None (undefined).
Examples
Creating an empty Headers object is simple:
js
const myHeaders = new Headers(); // Currently empty
You could add a header to this using Headers.append, then set a new
value for this header using set():
js
myHeaders.append("Content-Type", "image/jpeg");
myHeaders.set("Content-Type", "text/html");
If the specified header does not already exist, set() will create it and
set its value to the specified value. If the specified header does already exist and
does accept multiple values, set() will overwrite the existing value with
the new one:
js
myHeaders.set("Accept-Encoding", "deflate");
myHeaders.set("Accept-Encoding", "gzip");
myHeaders.get("Accept-Encoding"); // Returns 'gzip'
You'd need Headers.append to append the new value onto the values, not
overwrite it.
Specifications
| Specification |
|---|
| Fetch Standard # ref-for-dom-headers-set① |
Browser compatibility
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