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# Headers.set()

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.

## 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`.
