Jquery – replace or modify a function on a jQuery UI widget? How? (Monkey Patching)

jquerymonkeypatching

If I want to tweak some of the capability of a jQuery UI object, by replacing one of the functions, how would I go about doing that?

Example: suppose I wanted to modify the way the jQuery autocomplete widget rendered the suggestions. There's a method on the autocomplete object that looks like this:

_renderItem: function( ul, item) {
    return $( "<li></li>" )
        .data( "item.autocomplete", item )
        .append( "<a>" + item.label + "</a>" )
        .appendTo( ul );
},

Could I replace this?

I think this might be called Monkey Patching.

How? What syntax would I use?

Best Answer

I don't know about jQuery UI, but in general, this is how you redefine a function:

(function() {
   var _oldFunc = _renderItem;

   _renderItem = function(ul,item) {
      // do your thing
      // and optionally call the original function:
      return _oldFunc(ul,item);
   }
})();

The reason this is wrapped in an anonymous function is to create a closure for storing the original function. This way it can never interfere with global variables.

EDIT
To do this to a fn on a jQuery UI widget, use this syntax:

FYI: the way to grab the function is like this:

function monkeyPatchAutocomplete() { 

  // don't really need this, but in case I did, I could store it and chain 
  var oldFn = $.ui.autocomplete.prototype._renderItem; 

  $.ui.autocomplete.prototype._renderItem = function( ul, item) { 
     // whatever
  }; 
}

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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 .on('change') 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.

Best Answer

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