javascript – simple jquery file upload – How can I upload files asynchronously?

I would like to upload a file with jQuery asynchronously.

$(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: ");
            }
        });
    });
});

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/2.2.0/jquery.min.js"></script>
<span>File</span>
<input type="file" id="file" name="file" size="10"/>
<input id="uploadbutton" type="button" value="Upload"/>

• Use as little as

$('#one-specific-file').ajaxfileupload({
  'action': '/upload.php'
});

— Or as much as

$('input[type="file"]').ajaxfileupload({
  'action': '/upload.php',
  'params': {
    'extra': 'info'
  },
  'onComplete': function(response) {
    console.log('custom handler for file:');
    alert(JSON.stringify(response));
  },
  'onStart': function() {
    if(weWantedTo) return false; // cancels upload
  },
  'onCancel': function() {
    console.log('no file selected');
  }
});

<form id="upload-form">
    <div>
        <label for="file">File:</label>
        <input type="file" id="file" name="file" />
        <progress class="progress" value="0" max="100"></progress>
    </div>
    <hr />
    <input type="submit" value="Submit" />
</form>

.progress { display: none; }

$(document).ready(function(ev) {
    $("#upload-form").on('submit', (function(ev) {
        ev.preventDefault();
        $.ajax({
            xhr: function() {
                var progress = $('.progress'),
                    xhr = $.ajaxSettings.xhr();

                progress.show();

                xhr.upload.onprogress = function(ev) {
                    if (ev.lengthComputable) {
                        var percentComplete = parseInt((ev.loaded / ev.total) * 100);
                        progress.val(percentComplete);
                        if (percentComplete === 100) {
                            progress.hide().val(0);
                        }
                    }
                };

                return xhr;
            },
            url: 'upload.php',
            type: 'POST',
            data: new FormData(this),
            contentType: false,
            cache: false,
            processData: false,
            success: function(data, status, xhr) {
                // ...
            },
            error: function(xhr, status, error) {
                // ...
            }
       });
    }));
});

AJAX upload is difficult to use because the standard remote_form_for does not understand multi-part submissions. It won’t send the file data Rails requests back with the AJAX request.

Here’s the Rails code:

<% remote_form_for(:image_form, 
                   :url => { :controller => "blogs", :action => :create_asset }, 
                   :html => { :method => :post, 
                              :id => 'uploadForm', :multipart => true }) 
                                                                        do |f| %>
 Upload a file: <%= f.file_field :uploaded_data %>
<% end %>

Here is the JavaScript.

$('#uploadForm input').change(function(){
 $(this).parent().ajaxSubmit({
  beforeSubmit: function(a,f,o) {
   o.dataType = 'json';
  },
  complete: function(XMLHttpRequest, textStatus) {
   // XMLHttpRequest.responseText will contain the URL of the uploaded image.
   // Put it in an image element you create, or do with it what you will.
   // For example, if you have an image elemtn with id "my_image", then
   //  $('#my_image').attr('src', XMLHttpRequest.responseText);
   // Will set that image tag to display the uploaded image.
  },
 });
});

Here’s the Rails controller action. Pretty vanilla.

 @image = Image.new(params[:image_form])
 @image.save
 render :text => @image.public_filename