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Show image preview on upload -RAILS

i have been using Ruby on Rails (versions 2/3/4) and loved it because its so quick and saves the time to build website that normally require an year.
Recently i implemented uploading videos/music/images using paperclip,ffmpeg-paperclip and delayed_paperclip.i wanted to upload multiple images where i can see the uploaded images before submitting.So here is the code using paperclip and jquery where you can preview your uploaded images in a list format + a customised upload button(see below) instead of the traditional browse button for uploading files.
i am using bootstrap 3 and FontAwesome(for upload button icon)


Description:-

  1. In the form,i have input button of type file and added a style to give it a look as shown above which works good and responsively.
  2.  In the jquery,it detects for a change in upload button using change event listener and get all the uploaded file and lists it to the  div with id = list using li
  3. The code also has validations to show errors if non-image file is attached,file more than 1mb is attached and more than 5 files (for multiple uploads at once)
  4. Optional--you can also add a remove button on each uploaded image preview so that you can also remove the uploaded images and attach a new one instantly by using the $("id").remove
Lets start with the code
 
====================_form.html.erb

 <%= form_for(@user,:html=>{:multipart => true,:remote=>true,:class=>"form-horizontal",:role=>"form"}) do |f |%>

    <div class="col-lg-12">
      <a href="javascript:void(0);" class="upload btn">
        <i class="fa fa-upload fa-lg" style="padding-right: 5px"></i>
        Upload picture
        <%= f.file_field :avatar,:id=>"user_avatar",:multiple=>"true",:class=>"opacity"%></a>
        <span class="text-info"><small style="margin-left: 13px;">You can select 5 images at a time</small></span>

    <!-- show error here ->
      <p id="show_error" class=" col-md-offset-0" style="color: red; display: none;"></p>
  </div>

<!-- show uploaded images in list using col-lg-12 -->
    <div class="row text-success form-group">
    <ul id="list_images_places" style="list-style: none outside none;">

    </ul>
    </div>
<%end%>

=================my javascript:

$("#user_avatar").change(function(evt){

//remove the image onchange always
$('#list_images_places li').remove();
$("#show_error").html(" ").hide();
//check file type
var ext = $('#user_avatar').val().split('.').pop().toLowerCase();
if($.inArray(ext, ['gif','png','jpg','jpeg','tiff','bmp']) == -1) {
    $("#show_error").html("This is not an image file").show();
    //show no files selected
    $('#user_avatar').val("");
    return false;
}
     //get the file size and file type from file input field
       // var fsize = $('#i_file')[0].files[0].size;
        //var ftype = $('#i_file')[0].files[0].type;
        //var fname = $('#i_file')[0].files[0].name;
        //1048576--1MB
//check file size
   var file = $('#user_avatar')[0].files[0];
  if (file.size && file.size > 1048576) {
              $("#show_error").html("File size must be within 1 Mb or below").show();
                //show no files selected
              $('#user_avatar').val("");
              return false;  
            }

//check only 4 files uploaded at a time
var numFiles = $('#user_avatar')[0].files.length;
if (numFiles > 5){
     $("#show_error").html("Only 5 images can be uploaded at a time").show();
                //show no files selected
              $('#user_avatar').val("");
              return false;

}

<1--  code the add uplaoded images and show the listing in thumbnail format-->
    var files = evt.target.files; // FileList object

    // Loop through the FileList and render image files as thumbnails.
    for (var i = 0, f; f = files[i]; i++) {

      // Only process image files.
      if (!f.type.match('image.*')) {
        continue;
      }

      var reader = new FileReader();

      // Closure to capture the file information.
      reader.onload = (function(theFile) {
        return function(e) {
          // Render thumbnail.
          var li = document.createElement('li');
          li.innerHTML = ['<div style="width:100px !important;float:left !important;margin:10px;"><img class="thumb img-responsive" src="', e.target.result, '" title="', escape(theFile.name), '"/></div>'].join('');
                    document.getElementById('list_images_places').insertBefore(li, null);

        };
      })(f);

      // Read in the image file as a data URL.
      reader.readAsDataURL(f);
    }
  });


=================CSS style:

    .upload{
       padding: 8px 10px;
       position: relative;
       border-radius: 5px;
       width: auto !important;
    }
    .upload input[type="file"]{
    position: absolute;
    width: 100%;
    height: 100%;
    left: 0;
    top: 0;
    }
    .opacity{
     -ms-filter: "progid:DXImageTransform.Microsoft.Alpha(Opacity=0)";
      filter: alpha(opacity=0);
     -moz-opacity: 0;
     -khtml-opacity: 0;
     opacity: 0;
    }
    /*bootstrap*/
.well {
min-height: 20px;
padding: 19px;
margin-bottom: 20px;
background-color: whiteSmoke;
border: 1px solid #E3E3E3;
-webkit-border-radius: 4px;
-moz-border-radius: 4px;
border-radius: 4px;
-webkit-box-shadow: inset 0 1px 1px rgba(0, 0, 0, 0.05);
-moz-box-shadow: inset 0 1px 1px rgba(0, 0, 0, 0.05);
box-shadow: inset 0 1px 1px rgba(0, 0, 0, 0.05);
}
  .thumb {
    height: 75px;
    border: 1px solid #000;
    margin: 10px 5px 0 0;
    float: left;
  }

   
this is how it looks in action:

 The above code can be customized in the way you want and can be used with cross browsers as well.


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