How to create a jQuery plugin with methods?

Question

I'm trying to write a jQuery plugin that will provide additional functions/methods to the object that calls it. All the tutorials I read online (have been browsing for the past 2 hours) include, at the most, how to add options, but not additional functions.

Here's what I am looking to do:

//format div to be a message container by calling the plugin for that div

$("#mydiv").messagePlugin();
$("#mydiv").messagePlugin().saySomething("hello");

or something along those lines. Here's what it boils down to: I call the plugin, then I call a function associated with that plugin. I can't seem to find a way to do this, and I've seen many plugins do it before.

Here's what I have so far for the plugin:

jQuery.fn.messagePlugin = function() {
  return this.each(function(){
    alert(this);
  });

  //i tried to do this, but it does not seem to work
  jQuery.fn.messagePlugin.saySomething = function(message){
    $(this).html(message);
  }
};

How can I achieve something like that?

Thank you!

---

Update Nov 18, 2013: I've changed the correct answer to that of Hari's following comments and upvotes.

Answer 1

You can do:

(function ($) {

var YourPlugin = function (element, option) {
    var defaults = {
        //default value
    }

    this.option = $.extend({}, defaults, option);
    this.$element = $(element);
    this.init();
}

YourPlugin.prototype = {
    init: function () {
    },
    show: function() {

    },
    //another functions
}

$.fn.yourPlugin = function (option) {
    var arg = arguments,
        options = typeof option == 'object' && option;;
    return this.each(function () {
        var $this = $(this),
            data = $this.data('yourPlugin');

        if (!data) $this.data('yourPlugin', (data = new YourPlugin(this, options)));
        if (typeof option === 'string') {
            if (arg.length > 1) {
                data[option].apply(data, Array.prototype.slice.call(arg, 1));
            } else {
                data[option]();
            }
        }
    });
}; 
  });

In this way your plugins object is stored as data value in your element.

 //Initialization without option
 $('#myId').yourPlugin();

 //Initialization with option
 $('#myId').yourPlugin({
        //your option
 });

//call show method
$('#myId').yourPlugin('show');

Answer 2

Here i want to suggest steps to create simple plugin with arguments.

JS

(function($) {
    $.fn.myFirstPlugin = function( options ) {

        // Default params
        var params = $.extend({
            text     : 'Default Title',
            fontsize : 10,
        }, options);
        return $(this).text(params.text);

    }
}(jQuery));

Here, we have added default object called params and set default values of options using extend function. Hence, If we pass blank argument then it will set default values instead otherwise it will set.

HTML

$('.cls-title').myFirstPlugin({ text : 'Argument Title' });

Read more: How to Create JQuery plugin

Answer 3

Here is my bare-bones version of this. Similar to the ones posted before, you would call like:

$('#myDiv').MessagePlugin({ yourSettings: 'here' })
           .MessagePlugin('saySomething','Hello World!');

-or access the instance directly @ plugin_MessagePlugin

$elem = $('#myDiv').MessagePlugin();
var instance = $elem.data('plugin_MessagePlugin');
instance.saySomething('Hello World!');

MessagePlugin.js

;(function($){

    function MessagePlugin(element,settings){ // The Plugin
        this.$elem = element;
        this._settings = settings;
        this.settings = $.extend(this._default,settings);
    }

    MessagePlugin.prototype = { // The Plugin prototype
        _default: {
            message: 'Generic message'
        },
        initialize: function(){},
        saySomething: function(message){
            message = message || this._default.message;
            return this.$elem.html(message);
        }
    };

    $.fn.MessagePlugin = function(settings){ // The Plugin call

        var instance = this.data('plugin_MessagePlugin'); // Get instance

        if(instance===undefined){ // Do instantiate if undefined
            settings = settings || {};
            this.data('plugin_MessagePlugin',new MessagePlugin(this,settings));
            return this;
        }

        if($.isFunction(MessagePlugin.prototype[settings])){ // Call method if argument is name of method
            var args = Array.prototype.slice.call(arguments); // Get the arguments as Array
            args.shift(); // Remove first argument (name of method)
            return MessagePlugin.prototype[settings].apply(instance, args); // Call the method
        }

        // Do error handling

        return this;
    }

})(jQuery);

Answer 4

This can actually be made to work in a "nice" way using defineProperty. Where "nice" means without having to use () to get plugin namespace nor having to pass function name by string.

Compatibility nit: defineProperty doesn't work in ancient browsers such as IE8 and below. Caveat: $.fn.color.blue.apply(foo, args) won't work, you need to use foo.color.blue.apply(foo, args).

function $_color(color)
{
    return this.css('color', color);
}

function $_color_blue()
{
    return this.css('color', 'blue');
}

Object.defineProperty($.fn, 'color',
{
    enumerable: true,
    get: function()
    {
        var self = this;

        var ret = function() { return $_color.apply(self, arguments); }
        ret.blue = function() { return $_color_blue.apply(self, arguments); }

        return ret;
    }
});

$('#foo').color('#f00');
$('#bar').color.blue();

JSFiddle link

Answer 5

The problem with the currently selected answer is that you're not actually creating a new instance of the custom plugin for every element in the selector like you think you're doing... you're actually only creating a single instance and passing in the selector itself as the scope.

View this fiddle for a deeper explanation.

Instead, you'll need to loop through the selector using jQuery.each and instantiate a new instance of the custom plugin for every element in the selector.

Here's how:

(function($) {

    var CustomPlugin = function($el, options) {

        this._defaults = {
            randomizer: Math.random()
        };

        this._options = $.extend(true, {}, this._defaults, options);

        this.options = function(options) {
            return (options) ?
                $.extend(true, this._options, options) :
                this._options;
        };

        this.move = function() {
            $el.css('margin-left', this._options.randomizer * 100);
        };

    };

    $.fn.customPlugin = function(methodOrOptions) {

        var method = (typeof methodOrOptions === 'string') ? methodOrOptions : undefined;

        if (method) {
            var customPlugins = [];

            function getCustomPlugin() {
                var $el          = $(this);
                var customPlugin = $el.data('customPlugin');

                customPlugins.push(customPlugin);
            }

            this.each(getCustomPlugin);

            var args    = (arguments.length > 1) ? Array.prototype.slice.call(arguments, 1) : undefined;
            var results = [];

            function applyMethod(index) {
                var customPlugin = customPlugins[index];

                if (!customPlugin) {
                    console.warn('$.customPlugin not instantiated yet');
                    console.info(this);
                    results.push(undefined);
                    return;
                }

                if (typeof customPlugin[method] === 'function') {
                    var result = customPlugin[method].apply(customPlugin, args);
                    results.push(result);
                } else {
                    console.warn('Method \'' + method + '\' not defined in $.customPlugin');
                }
            }

            this.each(applyMethod);

            return (results.length > 1) ? results : results[0];
        } else {
            var options = (typeof methodOrOptions === 'object') ? methodOrOptions : undefined;

            function init() {
                var $el          = $(this);
                var customPlugin = new CustomPlugin($el, options);

                $el.data('customPlugin', customPlugin);
            }

            return this.each(init);
        }

    };

})(jQuery);

And a working fiddle.

You'll notice how in the first fiddle, all divs are always moved to the right the exact same number of pixels. That is because only one options object exists for all elements in the selector.

Using the technique written above, you'll notice that in the second fiddle, each div is not aligned and is randomly moved (excluding the first div as it's randomizer is always set to 1 on line 89). That is because we are now properly instantiating a new custom plugin instance for every element in the selector. Every element has its own options object and is not saved in the selector, but in the instance of the custom plugin itself.

This means that you'll be able to access the methods of the custom plugin instantiated on a specific element in the DOM from new jQuery selectors and aren't forced to cache them, as you would be in the first fiddle.

For example, this would return an array of all options objects using the technique in the second fiddle. It would return undefined in the first.

$('div').customPlugin();
$('div').customPlugin('options'); // would return an array of all options objects

This is how you would have to access the options object in the first fiddle, and would only return a single object, not an array of them:

var divs = $('div').customPlugin();
divs.customPlugin('options'); // would return a single options object

$('div').customPlugin('options');
// would return undefined, since it's not a cached selector

I'd suggest using the technique above, not the one from the currently selected answer.

Answer 6

I got it from jQuery Plugin Boilerplate

Also described in jQuery Plugin Boilerplate, reprise

// jQuery Plugin Boilerplate
// A boilerplate for jumpstarting jQuery plugins development
// version 1.1, May 14th, 2011
// by Stefan Gabos

// remember to change every instance of "pluginName" to the name of your plugin!
(function($) {

    // here we go!
    $.pluginName = function(element, options) {

    // plugin's default options
    // this is private property and is accessible only from inside the plugin
    var defaults = {

        foo: 'bar',

        // if your plugin is event-driven, you may provide callback capabilities
        // for its events. execute these functions before or after events of your
        // plugin, so that users may customize those particular events without
        // changing the plugin's code
        onFoo: function() {}

    }

    // to avoid confusions, use "plugin" to reference the
    // current instance of the object
    var plugin = this;

    // this will hold the merged default, and user-provided options
    // plugin's properties will be available through this object like:
    // plugin.settings.propertyName from inside the plugin or
    // element.data('pluginName').settings.propertyName from outside the plugin,
    // where "element" is the element the plugin is attached to;
    plugin.settings = {}

    var $element = $(element), // reference to the jQuery version of DOM element
    element = element; // reference to the actual DOM element

    // the "constructor" method that gets called when the object is created
    plugin.init = function() {

    // the plugin's final properties are the merged default and
    // user-provided options (if any)
    plugin.settings = $.extend({}, defaults, options);

    // code goes here

   }

   // public methods
   // these methods can be called like:
   // plugin.methodName(arg1, arg2, ... argn) from inside the plugin or
   // element.data('pluginName').publicMethod(arg1, arg2, ... argn) from outside
   // the plugin, where "element" is the element the plugin is attached to;

   // a public method. for demonstration purposes only - remove it!
   plugin.foo_public_method = function() {

   // code goes here

    }

     // private methods
     // these methods can be called only from inside the plugin like:
     // methodName(arg1, arg2, ... argn)

     // a private method. for demonstration purposes only - remove it!
     var foo_private_method = function() {

        // code goes here

     }

     // fire up the plugin!
     // call the "constructor" method
     plugin.init();

     }

     // add the plugin to the jQuery.fn object
     $.fn.pluginName = function(options) {

        // iterate through the DOM elements we are attaching the plugin to
        return this.each(function() {

          // if plugin has not already been attached to the element
          if (undefined == $(this).data('pluginName')) {

              // create a new instance of the plugin
              // pass the DOM element and the user-provided options as arguments
              var plugin = new $.pluginName(this, options);

              // in the jQuery version of the element
              // store a reference to the plugin object
              // you can later access the plugin and its methods and properties like
              // element.data('pluginName').publicMethod(arg1, arg2, ... argn) or
              // element.data('pluginName').settings.propertyName
              $(this).data('pluginName', plugin);

           }

        });

    }

})(jQuery);