**File upload** is a common feature in many web applications that was originally done using web forms with #key# enctype: `multipart/form-data` #key#. However, with the growing use of Single Page Applications,  which run on AJAX requests, Ajax file upload has become necessary. In this Edpresso shot, you'll learn how to upload files using Ajax.



# Example: Ajax file upload 
The example below shows a file picker that returns the size of uploaded files. 


<html>
 <head>
 </head>
 <body>
  <form>
    <h1>File Size Inspector</h1>
    <input id="file_picker" type="file" />
  </form>
 </body>
</html>

codemirror

console

# How it works
First, an `onchange` event listener is attached to the file picker:

Then, the file is obtained from the event object the listener provides -- the first file in the files array is picked because we are dealing with single files.

Next, an Ajax call is made to the endpoint that expects a file upload. In this case, the file is: `https://express-file-server.vicradon.repl.co/upload`.

Further logic, like notifying, the user can be done in the `.then` block. If any HTTP errors are encountered, they are handled in the `.catch` block.

How to upload a file using Ajax

Upload files using Ajax by attaching an `onchange` event listener to the file picker, obtaining the file, and making an Ajax call to the server. Handle results in `.then` and `.catch` blocks.