FormData()

The FormData() constructor creates a new FormData object.

var formData = new FormData(form)

form Optional

An HTML <form> element — when specified, the FormData object will be populated with the form's current keys/values using the name property of each element for the keys and their submitted value for the values. It will also encode file input content.

The following line creates an empty FormData object:

var formData = new FormData(); // Currently empty

You could add a key/value pair to this using FormData.append:

formData.append('username', 'Chris');

Or you can specify the optional form argument when creating the FormData object, to prepopulate it with values from the specified form:

<form id="myForm" name="myForm">
  <div>
    <label for="username">Enter name:</label>
    <input type="text" id="username" name="username">
  </div>
  <div>
    <label for="useracc">Enter account number:</label>
    <input type="text" id="useracc" name="useracc">
  </div>
  <div>
    <label for="userfile">Upload file:</label>
    <input type="file" id="userfile" name="userfile">
  </div>
  <input type="submit" value="Submit!">
</form>

let myForm = document.getElementById('myForm');
let formData = new FormData(myForm);

• XMLHTTPRequest
• Using XMLHttpRequest
• Using FormData objects
• <form>