How can I upload files asynchronously?

 

I would like to upload a file asynchronously with jQuery. This is my HTML: 

<span>File</span>
<input type="file" id="file" name="file" size="10"/>
<input id="uploadbutton" type="button" value="Upload"/>

And here my Jquery code: 

$(document).ready(function () {
    $("#uploadbutton").click(function () {
        var filename = $("#file").val();

        $.ajax({
            type: "POST",
            url: "addFile.do",
            enctype: 'multipart/form-data',
            data: {
                file: filename
            },
            success: function () {
                alert("Data Uploaded: ");
            }
        });
    });
});

Instead of the file being uploaded, I am only getting the filename. What can I do to fix this problem?

Current Solution

I am using the jQuery Form Plugin to upload files.

With HTML5 you can make file uploads with Ajax and jQuery. Not only that, you can do file validations (name, size, and MIME type) or handle the progress event with the HTML5 progress tag (or a div). Recently I had to make a file uploader, but I didn't want to use Flash nor Iframes or plugins and after some research I came up with the solution.

The HTML: 

<form enctype="multipart/form-data">
    <input name="file" type="file" />
    <input type="button" value="Upload" />
</form>
<progress></progress>

First, you can do some validation if you want. For example, in the onChange event of the file: 

$(':file').on('change', function() {
    var file = this.files[0];
    if (file.size > 1024) {
        alert('max upload size is 1k')
    }

    // Also see .name, .type
});

Now the Ajax submit with the button's click: 

$(':button').on('click', function() {
    $.ajax({
        // Your server script to process the upload
        url: 'upload.php',
        type: 'POST',

        // Form data
        data: new FormData($('form')[0]),

        // Tell jQuery not to process data or worry about content-type
        // You *must* include these options!
        cache: false,
        contentType: false,
        processData: false,

        // Custom XMLHttpRequest
        xhr: function() {
            var myXhr = $.ajaxSettings.xhr();
            if (myXhr.upload) {
                // For handling the progress of the upload
                myXhr.upload.addEventListener('progress', function(e) {
                    if (e.lengthComputable) {
                        $('progress').attr({
                            value: e.loaded,
                            max: e.total,
                        });
                    }
                } , false);
            }
            return myXhr;
        }
    });
});

As you can see, with HTML5 (and some research) file uploading not only becomes possible but super easy. Try it with Google Chrome as some of the HTML5 components of the examples aren't available in every browser.

There are various ready-made plugins on doing file upload for jQuery.

Doing this kind of uploading hacks is not an enjoyable experience, so people enjoy using ready-made solutions.

Here's few:

  • JQuery File Uploader
  • Multiple File Upload Plugin
  • Mini Multiple File Upload
  • jQuery File Upload

    • You can search for more projects on NPM (using "jquery-plugin" as the keyword) or on Github.

    2017 Update: It still depends on the browsers your demographic uses.

    An important thing to understand with the "new" HTML5 file API is that is wasn't supported until IE 10. If the specific market you're aiming at has a higher-than-average prepensity toward older versions of Windows, you might not have access to it.

    Going into 2017, about 5% of browsers are one of IE 6, 7, 8 or 9. If you head into a big corporation (eg this is a B2B tool, or something you're delivering for training) that number can rocket. Just a few months ago —in 2016— I dealt with a company using IE8 on over 60% of their machines.

    So before you do anything: check what browser your users use . If you don't, you'll learn a quick and painful lesson in why "works for me" isn't good enough in a deliverable to a client.

    My answer from 2008 follows.

    However, there are viable non-JS methods of file uploads. You can create an iframe on the page (that you hide with CSS) and then target your form to post to that iframe. The main page doesn't need to move.

    It's a "real" post so it's not wholly interactive. If you need status you need something server-side to process that. This varies massively depending on your server. ASP.NET has nicer mechanisms. PHP plain fails, but you can use Perl or Apache modifications to get around it.

    If you need multiple file-uploads, it's best to do each file one at a time (to overcome maximum file upload limits). Post the first form to the iframe, monitor its progress using the above and when it has finished, post the second form to the iframe, and so on.

    Or use a Java/Flash solution. They're a lot more flexible in what they can do with their posts...

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