Easy mixins for jQuery.
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Easy states and mixins for jQuery objects.

Why use jQuery.instance?

When creating interfaces with complicated JavaScript behavior, things can get really complicated real quick. Sometimes, doing things the OOP way can be a very sane solution.

You can easily extend an object like so:

var $sidebar = $("#sidebar");
$sidebar.load = function() { /* ... */ };

...but if you were to access that in another area of your script, it'd be another object altogether and your extensions will not be available.

$("a.reload-sidebar").click(function() {
    var $sb = $("#sidebar");
    $sb.load();       // Error: `load` is not defined
    $sidebar == $sb;  // false

If you were to use $("#sidebar").instance() instead, you'll be sure that $sb and $sidebar will be the same object.

var $sidebar = $("#sidebar").instance();
$sidebar.load = function() { /* ... */ };

$("a.reload-sidebar").click(function() {
    var $sb = $("#sidebar").instance();
    $sidebar == $sb;  // true


Use .instance() to make sure that there will only be one instance of an object.

var $one = $("#sidebar").instance();
$one.abc = 42;

var $two = $("#sidebar").instance(); // will be the same as $one
$two.abc;      // 42
$one == $two;  // true
$two.show();   // still a jQuery object equivalent to $("#sidebar")

It can also be used for making 'pseudo-classes' for jQuery objects by letting you extend your objects with methods and properties from another object (a 'mixin').

// This is a mixin with properties/methods that will be added
// to a jQuery object.
var Sidebar = {
  name: 'My sidebar',
  expand: function () {

// Calling $(x).instance(Sidebar) is the same as:
// $(x).instance().extend(Sidebar);
var $one = $("#sidebar").instance(Sidebar);
$one.name;      // 'My sidebar'

var $two = $("#sidebar").instance();
$two.expand();  // Same as $one.expand()

Hypothetical example

Let's say that we're to create a spin button widget. We can have a function that returns a jQuery object like this:

var $spin = $.spinbutton(); // Returns a jQuery object

But we'd also want that object to be able to keep a state (i.e., variables), and have some custom functions like so:

$spin.comment = "Hello";

From here, $.spinbutton can be simply a $("...") generator that, in the end, will call instance() to extend the object:

$.spinbutton = function() {
  var $button = $("<div class='spin-button'>")
      .append($("<span class='display'>"))
      .append($("<a class='add'>")
          .click(function() { $this.add(); return false; }))
      .append($("<a class='subtract'>")
          .click(function() { $this.subtract(); return false; }))

  return $button.instance(SpinButton);

And the mixin can look like this:

var SpinButton = {
  $display: function () { return this.find('span.display'); },
  setValue: function (val) { this.$display().html(val); },
  getValue: function () { return parseInt(this.$display().html()); },
  add:      function () { this.setValue(this.getValue + 1); },
  subtract: function () { this.setValue(this.getValue - 1); }

Now, the functions can be used elsewhere!

/* Elsewhere */ {
    var $button = $("#container .spin-button").instance();

Without the .instance(), the $("#container .spin-button") will simply return a jQuery object /without/ the mixin we defined. Calling .instance() will return the very same JavaScript object that was created earlier, maintaining it's state and mixins.


jQuery.instance is authored and maintained by Rico Sta. Cruz of Sinefunc, Inc. See more of our work on www.sinefunc.com!


(c) 2010 Rico Sta. Cruz and Sinefunc, Inc. See the LICENSE file for more details.