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# FormData.append()

The **`append()`** method of the `FormData` interface appends a new value onto an existing key inside a `FormData` object, or adds the key if it does not already exist.

## Syntax

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

### Parameters

- `name`
  - : The name of the field whose data is contained in `value`.
- `value`
  - : The value of the field. This can be a string or a `Blob` (including subclasses such as `File`). If none of these, the value is converted to a string.
- `filename` _**optional**_
  - : The filename reported to the server when a `Blob` or `File` is passed as the second parameter. The default filename for `Blob` objects is "blob". The default filename for `File` objects is the file's filename.

### Return value

`undefined`
