Sending multipart/formdata with jQuery.ajax

Starting with Safari 5/Firefox 4, it’s easiest to use the FormData class:

var data = new FormData();jQuery.each(jQuery('#file')[0].files, function(i, file) {    data.append('file-'+i, file);});

So now you have a FormData object, ready to be sent along with the XMLHttpRequest.

jQuery.ajax({    url: 'php/upload.php',    data: data,    cache: false,    contentType: false,    processData: false,    method: 'POST',    type: 'POST', // For jQuery < 1.9    success: function(data){        alert(data);    }});

It’s imperative that you set the contentType option to false, forcing jQuery not to add a Content-Type header for you, otherwise, the boundary string will be missing from it.Also, you must leave the processData flag set to false, otherwise, jQuery will try to convert your FormData into a string, which will fail.

You may now retrieve the file in PHP using:

$_FILES['file-0']

(There is only one file, file-0, unless you specified the multiple attribute on your file input, in which case, the numbers will increment with each file.)

Using the FormData emulation for older browsers

var opts = {    url: 'php/upload.php',    data: data,    cache: false,    contentType: false,    processData: false,    method: 'POST',    type: 'POST', // For jQuery < 1.9    success: function(data){        alert(data);    }};if(data.fake) {    // Make sure no text encoding stuff is done by xhr    opts.xhr = function() { var xhr = jQuery.ajaxSettings.xhr(); xhr.send = xhr.sendAsBinary; return xhr; }    opts.contentType = "multipart/form-data; boundary="+data.boundary;    opts.data = data.toString();}jQuery.ajax(opts);

Create FormData from an existing form

Instead of manually iterating the files, the FormData object can also be created with the contents of an existing form object:

var data = new FormData(jQuery('form')[0]);

Use a PHP native array instead of a counter

Just name your file elements the same and end the name in brackets:

jQuery.each(jQuery('#file')[0].files, function(i, file) {    data.append('file[]', file);});

$_FILES['file'] will then be an array containing the file upload fields for every file uploaded. I actually recommend this over my initial solution as it’s simpler to iterate over.

Look at my code, it does the job for me

$( '#formId' )  .submit( function( e ) {    $.ajax( {      url: 'FormSubmitUrl',      type: 'POST',      data: new FormData( this ),      processData: false,      contentType: false    } );    e.preventDefault();  } );

Just wanted to add a bit to Raphael's great answer. Here's how to get PHP to produce the same $_FILES, regardless of whether you use JavaScript to submit.

HTML form:

<form enctype="multipart/form-data" action="/test.php" method="post" class="putImages">   <input name="media[]" type="file" multiple/>   <input class="button" type="submit" alt="Upload" value="Upload" /></form>

PHP produces this $_FILES, when submitted without JavaScript:

Array(    [media] => Array        (            [name] => Array                (                    [0] => Galata_Tower.jpg                    [1] => 518f.jpg                )            [type] => Array                (                    [0] => image/jpeg                    [1] => image/jpeg                )            [tmp_name] => Array                (                    [0] => /tmp/phpIQaOYo                    [1] => /tmp/phpJQaOYo                )            [error] => Array                (                    [0] => 0                    [1] => 0                )            [size] => Array                (                    [0] => 258004                    [1] => 127884                )        ))

If you do progressive enhancement, using Raphael's JS to submit the files...

var data = new FormData($('input[name^="media"]'));     jQuery.each($('input[name^="media"]')[0].files, function(i, file) {    data.append(i, file);});$.ajax({    type: ppiFormMethod,    data: data,    url: ppiFormActionURL,    cache: false,    contentType: false,    processData: false,    success: function(data){        alert(data);    }});

... this is what PHP's $_FILES array looks like, after using that JavaScript to submit:

Array(    [0] => Array        (            [name] => Galata_Tower.jpg            [type] => image/jpeg            [tmp_name] => /tmp/phpAQaOYo            [error] => 0            [size] => 258004        )    [1] => Array        (            [name] => 518f.jpg            [type] => image/jpeg            [tmp_name] => /tmp/phpBQaOYo            [error] => 0            [size] => 127884        ))

That's a nice array, and actually what some people transform $_FILES into, but I find it's useful to work with the same $_FILES, regardless if JavaScript was used to submit. So, here are some minor changes to the JS:

// match anything not a [ or ]regexp = /^[^[\]]+/;var fileInput = $('.putImages input[type="file"]');var fileInputName = regexp.exec( fileInput.attr('name') );// make files availablevar data = new FormData();jQuery.each($(fileInput)[0].files, function(i, file) {    data.append(fileInputName+'['+i+']', file);});

(14 April 2017 edit: I removed the form element from the constructor of FormData() -- that fixed this code in Safari.)

That code does two things.

1. Retrieves the input name attribute automatically, making the HTML more maintainable. Now, as long as form has the class putImages, everything else is taken care of automatically. That is, the input need not have any special name.
2. The array format that normal HTML submits is recreated by the JavaScript in the data.append line. Note the brackets.

With these changes, submitting with JavaScript now produces precisely the same $_FILES array as submitting with simple HTML.