File upload using ajax

form.html.erb

<!-- This is the form with data remote true and include jquery.form.js file in assets-->

<%=form_for @image, remote: true, html: {id: 'image_form'} do |f|%>
    <%= f.file_field :image %>
    <%= f.submit, onlclick: "submitForm(); return false;" %>
<%end%>
<!-- form end -->


<!-- Script for submit form -->

<script type="text/javascript">
  function submitForm(){
    $("form#image_form").ajaxForm().submit();
  }
</script>

<!-- script end -->

jquery.form.js

// AMD support
(function (factory) {
    "use strict";
    if (typeof define === 'function' && define.amd) {
        // using AMD; register as anon module
        define(['jquery'], factory);
    } else {
        // no AMD; invoke directly
        factory( (typeof(jQuery) != 'undefined') ? jQuery : window.Zepto );
    }
}

(function($) {
"use strict";


/**
 * Feature detection
 */
var feature = {};
feature.fileapi = $("<input type='file'/>").get(0).files !== undefined;
feature.formdata = window.FormData !== undefined;

var hasProp = !!$.fn.prop;

// attr2 uses prop when it can but checks the return type for
// an expected string.  this accounts for the case where a form 
// contains inputs with names like "action" or "method"; in those
// cases "prop" returns the element
$.fn.attr2 = function() {
    if ( ! hasProp ) {
        return this.attr.apply(this, arguments);
    }
    var val = this.prop.apply(this, arguments);
    if ( ( val && val.jquery ) || typeof val === 'string' ) {
        return val;
    }
    return this.attr.apply(this, arguments);
};

/**
 * ajaxSubmit() provides a mechanism for immediately submitting
 * an HTML form using AJAX.
 */
$.fn.ajaxSubmit = function(options) {
    /*jshint scripturl:true */

    // fast fail if nothing selected (http://dev.jquery.com/ticket/2752)
    if (!this.length) {
        log('ajaxSubmit: skipping submit process - no element selected');
        return this;
    }

    var method, action, url, $form = this;

    if (typeof options == 'function') {
        options = { success: options };
    }
    else if ( options === undefined ) {
        options = {};
    }

    method = options.type || this.attr2('method');
    action = options.url  || this.attr2('action');

    url = (typeof action === 'string') ? $.trim(action) : '';
    url = url || window.location.href || '';
    if (url) {
        // clean url (don't include hash vaue)
        url = (url.match(/^([^#]+)/)||[])[1];
    }

    options = $.extend(true, {
        url:  url,
        success: $.ajaxSettings.success,
        type: method || $.ajaxSettings.type,
        iframeSrc: /^https/i.test(window.location.href || '') ? 'javascript:false' : 'about:blank'
    }, options);

    // hook for manipulating the form data before it is extracted;
    // conveni

Usage Note

 Usage Note:
-----------

// Just put this file in assets/javascripts and require it in application.js
// call function ajaxForm() on id of form containing file while submitting.

Do not use both ajaxSubmit and ajaxForm on the same form. These
functions are mutually exclusive. Use ajaxSubmit if you want
to bind your own submit handler to the form. For example,
 
$(document).ready(function() {
$('#myForm').on('submit', function(e) {
e.preventDefault(); // <-- important
$(this).ajaxSubmit({
target: '#output'
});
});
});
 
Use ajaxForm when you want the plugin to manage all the event binding
for you. For example,
 
$(document).ready(function() {
$('#myForm').ajaxForm({
target: '#output'
});
});
 
You can also use ajaxForm with delegation (requires jQuery v1.7+), so the
form does not have to exist when you invoke ajaxForm:
 
$('#myForm').ajaxForm({
delegation: true,
target: '#output'
});
 
When using ajaxForm, the ajaxSubmit function will be invoked for you
at the appropriate time.