Manually uploading files via AJAX

To upload a file via AJAX (e.g. from an <input type='file'>) you need to wrap your params in a FormData Archive object.

You can initialize a FormData using the contents of a form:

var form = document.querySelector('') // Find the <form> element
var formData = new FormData(form); // Wrap form contents

Or you can construct it manually, param by param:

var fileInput = document.querySelector('form input[type=file]');
var attachment = fileInput.files[0];

var formData = new FormData(); 
formData.append('email', '');
formData.append('attachment', attachment, 'filename.jpg');

You can now send your FormData via AJAX like this:

var request = new XMLHttpRequest();'POST', '/my/url', true);
request.onload = function() { console.log("Server responded with %o", request.responseText) };

In jQuery you would send it like this:

  url: '/my/url',
  type: 'POST',
  data: formData,
  contentType: false,
  processData: false

Note the contentType and processData options, which are needed so that jQuery does not try to serialize the FormData object.

Supporting legacy browsers

Short story:

  • The solution above works in IE 10
  • I recommend to offer a standard, non-AJAX form for older IEs
  • All other solutions will bring you pain and long nights

Long story:

Also see Dynamically uploading files to Rails with jQuery File Upload.

Henning Koch about 6 years ago
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