# How to use the FormData object

> Learn what the FormData object is and how to use it to send form fields and files with fetch, using append(), get() and set() to build a multipart body.

Author: [Flavio Copes](https://flaviocopes.com/about/) | Published: 2022-06-05 | Topics: [Web Platform](https://flaviocopes.com/tags/platform/) | Canonical: https://flaviocopes.com/formdata/

The `FormData` object is used to store form input fields values.

It's especially useful when you need to send files to the server.

It's probably the only time you'll actually need it.

Here is one example of using FormData to send the content of a file using fetch.

We have an input field:

```html
<input type="file" id="fileUpload" />
```

We attach a `change` event handler on it:

```js
document.querySelector('#fileUpload').addEventListener('change', (event) => {
  handleImageUpload(event)
})
```

and we manage the bulk of our logic in the `handleImageUpload()` function:

```js
const handleImageUpload = (event) => {
  const files = event.target.files
  const formData = new FormData()
  formData.append('myFile', files[0])

  fetch('/saveImage', {
    method: 'POST',
    body: formData,
  })
    .then((response) => response.json())
    .then((data) => {
      console.log(data)
    })
    .catch((error) => {
      console.error(error)
    })
}
```

In this example we POST to the `/saveImage` endpoint.

You could send more data too by appending it to the `formData` object.

In the server-side, to access the file data you must parse the request as a multipart form.

See for example [how to upload files in a Next.js form](https://flaviocopes.com/nextjs-upload-files/)

The FormData object you create has many useful methods:

- `append()` to add a value to the object, with the specified key. If the key already exists, the value is added to that key, without eliminating the first one
- `delete()` deletes a key value pair
- `entries()` gives an Iterator object you can loop to list the key value pairs hosted
- `get()` get the value associated with a key. If more than one value was appended, it returns the first one
- `getAll()` get all the values associated with a key
- `has()` returns true if there's a key
- `keys()` gives an Iterator object you can loop to list the keys hosted
- `set()` to add a value to the object, with the specified key. If the key already exists, the value is replaced
- `values()` gives an Iterator object you can loop to list the values hosted

The FormData object is part of the [XMLHttpRequest 2](https://flaviocopes.com/xhr/) spec.

It's available in [all the modern browsers](http://caniuse.com/#feat=xhr2) and it's most often used when sending images through fetch.

See [how to handle images uploaded server-side](https://flaviocopes.com/how-to-handle-file-uploads-node/)