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# Headers.append()

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.prototype.set()` and `append()` is
that if the specified header already exists and accepts multiple values,
`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.

## Syntax

```js
append(name, value)
```

### Parameters

- `name`
  - : The name of the HTTP header you want to add to the `Headers` object.
- `value`
  - : The value of the HTTP header you want to add.

### Return value

None (`undefined`).
