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Version: 3.34.0

FormData()

The FormData() constructor creates a new FormData object.

Syntax​

new FormData()
new FormData(form)

Note: FormData() can only be constructed with new. Attempting to call it without new throws a TypeError.

Parameters​

  • form optional
    • : An HTML <form> element — when specified, the FormData object will be populated with the form's current key/value pairs using the name property of each element for the keys and their submitted value for the values. File input elements are handled specially: their values are taken from the files selected by the user in the upload control.

Return value​

A new FormData object, pre-populated with form data if the optional form parameter was provided.

Description​

The FormData interface provides a way to construct a set of key/value pairs representing form fields and their values, which can be sent using methods such as fetch(). It uses the same format a form would use if the encoding type were set to "multipart/form-data".

You can also append additional data to the FormData object after it's created using its various methods.

A FormData object can be used in a number of ways with other APIs:

  1. It can be sent with the fetch() API
  2. It works seamlessly with the Request and Response objects - it can be used directly as the body of a Request object
  3. It can be obtained from a Response object using the formData() method
  4. It can be passed directly to the URLSearchParams constructor

The transmitted data is in the same format that the form's submit() method would use to send the data if the form's encoding type were set to "multipart/form-data".