[Fuente: http://docs.jquery.com/Plugins/Authoring]
Extender jQuery con plugins y métodos es muy potente y puede ahorrarte mucho tiempo de desarrollo por medio de abstraer las funciones complejas dentro de plugins. Explicaremos aqui lo básico, las mejores prácticas y los fallos más comunes
Primeros pasos
Para escribir un plugin de jQuery , empieza añadiendo una nueva propiedad de función al objeto jQuery.fn donde el nombre de la propiedad es el nombre de tu plugin:
jQuery.fn.myPlugin = function() {
// Do your awesome plugin stuff here
};
Cuidao! Dónde está el símbolo del dolar que tanto queremos? Está aún ahí , pero para asegurarnos que tu plugin no colisiona con otras librerias que utilicen el símbolo del dolar, la mejor práctica es pasar jQuery a un IIFE (Immediately Invoked Function Expression) que lo mapea al símbolo del dolar de forma que no puede ser sobreescrito por otra librería en ese ámbito.
(function( $ ) {
$.fn.myPlugin = function() {
// Do your awesome plugin stuff here
};
})( jQuery );
Así mejor. De esta forma , dentro de esa función IIFE podemos utilizar el dolar con total tranquilidad.
Contexto
Ahora que tenemos nuestra interfaz lista podemos empezar a escribir el código del plugin. Pero antes de eso, comentamos algo importante sobre el contexto. En el ámbito inmediato de la función del plugin, la palabra clave this se refiere al objeto jQuery sobre el que se invocó el método del plugin. Es un error muy común confundirlo con los casos donde jQuery accepta una función de callback, y aqui el this se refiere al elemento DOM nativo. Esto hace que muchas veces los programadores de forma innecesaria hagan un wrapping de la palabra clave this en la función jQuery.
(function( $ ){
$.fn.myPlugin = function() {
// there's no need to do $(this) because
// "this" is already a jquery object
// $(this) would be the same as $($('#element'));
this.fadeIn('normal', function(){
// the this keyword is a DOM element
});
};
})( jQuery );
$('#element').myPlugin();
Lo básico
Ahora que entendemos el contexto de los plugins de jQuery , escribamos un plugin que haga algo:
(function( $ ){
$.fn.maxHeight = function() {
var max = 0;
this.each(function() {
max = Math.max( max, $(this).height() );
});
return max;
};
})( jQuery );
var tallest = $('div').maxHeight(); // Returns the height of the tallest div
Este plugin simplemente el div que tenga la altura máxima dentro de la página.
Manteniendo la capacidad de encadenamiento
The previous example returns an integer value of the tallest div on the page, but often times the intent of a plugin is simply modify the collection of elements in some way, and pass them along to the next method in the chain. This is the beauty of jQuery’s design and is one of the reasons jQuery is so popular. So to maintain chainability in a plugin, you must make sure your plugin returns thethis keyword.
(function( $ ){
$.fn.lockDimensions = function( type ) {
return this.each(function() {
var $this = $(this);
if ( !type || type == 'width' ) {
$this.width( $this.width() );
}
if ( !type || type == 'height' ) {
$this.height( $this.height() );
}
});
};
})( jQuery );
$('div').lockDimensions('width').css('color', 'red');
Because the plugin returns the this keyword in its immediate scope, it maintains chainability and the jQuery collection can continue to be manipulated by jQuery methods, such as .css. So if your plugin doesn’t return an intrinsic value, you should always return the this keyword in the immediate scope of the plugin function. Also, as you might assume, arguments you pass in your plugin invocation get passed to the immediate scope of the plugin function. So in the previous example, the string ‘width’ becomes the type argument for the plugin function.
Defaults and Options
For more complex and customizable plugins that provide many options, it’s a best practice to have default settings that can get extended (using $.extend) when the plugin is invoked. So instead of calling a plugin with a large number of arguments, you can call it with one argument which is an object literal of the settings you would like to override. Here’s how you do it.
(function( $ ){
$.fn.tooltip = function( options ) {
// Create some defaults, extending them with any options that were provided
var settings = $.extend( {
'location' : 'top',
'background-color' : 'blue'
}, options);
return this.each(function() {
// Tooltip plugin code here
});
};
})( jQuery );
$('div').tooltip({
'location' : 'left'
});
In this example, after calling the tooltip plugin with the given options, the default location setting gets overridden to become 'left', while the background-color setting remains the default'blue'. So the final settings object ends up looking like this:
{
'location' : 'left',
'background-color' : 'blue'
}
This is a great way to offer a highly configurable plugin without requiring the developer to define all available options.
Namespacing
Properly namespacing your plugin is a very important part of plugin development. Namespacing correctly assures that your plugin will have a very low chance of being overwritten by other plugins or code living on the same page. Namespacing also makes your life easier as a plugin developer because it helps you keep better track of your methods, events and data.
Plugin Methods
Under no circumstance should a single plugin ever claim more than one namespace in thejQuery.fn object.
(function( $ ){
$.fn.tooltip = function( options ) {
// THIS
};
$.fn.tooltipShow = function( ) {
// IS
};
$.fn.tooltipHide = function( ) {
// BAD
};
$.fn.tooltipUpdate = function( content ) {
// !!!
};
})( jQuery );
This is a discouraged because it clutters up the $.fn namespace. To remedy this, you should collect all of your plugin’s methods in an object literal and call them by passing the string name of the method to the plugin.
(function( $ ){
var methods = {
init : function( options ) {
// THIS
},
show : function( ) {
// IS
},
hide : function( ) {
// GOOD
},
update : function( content ) {
// !!!
}
};
$.fn.tooltip = function( method ) {
// Method calling logic
if ( methods[method] ) {
return methods[ method ].apply( this, Array.prototype.slice.call( arguments, 1 ));
} else if ( typeof method === 'object' || ! method ) {
return methods.init.apply( this, arguments );
} else {
$.error( 'Method ' + method + ' does not exist on jQuery.tooltip' );
}
};
})( jQuery );
// calls the init method
$('div').tooltip();
// calls the init method
$('div').tooltip({
foo : 'bar'
});
// calls the hide method
$('div').tooltip('hide');
// calls the update method
$('div').tooltip('update', 'This is the new tooltip content!');
This type of plugin architecture allows you to encapsulate all of your methods in the plugin’s parent closure, and call them by first passing the string name of the method, and then passing any additional parameters you might need for that method. This type of method encapsulation and architecture is a standard in the jQuery plugin community and it used by countless plugins, including the plugins and widgets in jQueryUI .
Events
A lesser known feature of the bind method is that is allows for namespacing of bound events. If your plugin binds an event, its a good practice to namespace it. This way, if you need to unbind it later, you can do so without interfering with other events that might have been bound to the same type of event. You can namespace your events by appending “.<namespace>” to the type of event you’re binding.
(function( $ ){
var methods = {
init : function( options ) {
return this.each(function(){
$(window).bind('resize.tooltip', methods.reposition);
});
},
destroy : function( ) {
return this.each(function(){
$(window).unbind('.tooltip');
})
},
reposition : function( ) {
// ...
},
show : function( ) {
// ...
},
hide : function( ) {
// ...
},
update : function( content ) {
// ...
}
};
$.fn.tooltip = function( method ) {
if ( methods[method] ) {
return methods[method].apply( this, Array.prototype.slice.call( arguments, 1 ));
} else if ( typeof method === 'object' || ! method ) {
return methods.init.apply( this, arguments );
} else {
$.error( 'Method ' + method + ' does not exist on jQuery.tooltip' );
}
};
})( jQuery );
$('#fun').tooltip();
// Some time later...
$('#fun').tooltip('destroy');
In this example, when the tooltip is initialized with the init method, it binds the reposition method to the resize event of the window under the namespace ‘tooltip’. Later, if the developer needs to destroy the tooltip, we can unbind the events bound by the plugin by passing its namespace, in this case ‘tooltip’, to the unbind method. This allows us to safely unbind plugin events without accidentally unbinding events that may have been bound outside of the plugin.
Data
Often times in plugin development, you may need to maintain state or check if your plugin has already been initialized on a given element. Using jQuery’s data method is a great way to keep track of variables on a per element basis. However, rather than keeping track of a bunch of separate data calls with different names, it’s best to use a single object literal to house all of your variables, and access that object by a single data namespace.
(function( $ ){
var methods = {
init : function( options ) {
return this.each(function(){
var $this = $(this),
data = $this.data('tooltip'),
tooltip = $('<div />', {
text : $this.attr('title')
});
// If the plugin hasn't been initialized yet
if ( ! data ) {
/*
Do more setup stuff here
*/
$(this).data('tooltip', {
target : $this,
tooltip : tooltip
});
}
});
},
destroy : function( ) {
return this.each(function(){
var $this = $(this),
data = $this.data('tooltip');
// Namespacing FTW
$(window).unbind('.tooltip');
data.tooltip.remove();
$this.removeData('tooltip');
})
},
reposition : function( ) { // ... },
show : function( ) { // ... },
hide : function( ) { // ... },
update : function( content ) { // ...}
};
$.fn.tooltip = function( method ) {
if ( methods[method] ) {
return methods[method].apply( this, Array.prototype.slice.call( arguments, 1 ));
} else if ( typeof method === 'object' || ! method ) {
return methods.init.apply( this, arguments );
} else {
$.error( 'Method ' + method + ' does not exist on jQuery.tooltip' );
}
};
})( jQuery );
Using data helps you keep track of variables and state across method calls from your plugin. Namespacing your data into one object literal makes it easy to access all of your plugin’s properties from one central location, as well as reducing the data namespace which allows for easy removal if need be.
Summary and Best Practices
Writing jQuery plugins allows you to make the most out of the library and abstract your most clever and useful functions out into reusable code that can save you time and make your development even more efficient. Here’s a brief summary of the post and what to keep in mind when developing your next jQuery plugin:
- Always wrap your plugin in a closure:
(function( $ ){ /* plugin goes here */ })( jQuery ); - Don’t redundantly wrap the
thiskeyword in the immediate scope of your plugin’s function - Unless you’re returning an intrinsic value from your plugin, always have your plugin’s function return the
thiskeyword to maintain chainability. - Rather than requiring a lengthy amount of arguments, pass your plugin settings in an object literal that can be extended over the plugin’s defaults.
- Don’t clutter the
jQuery.fnobject with more than one namespace per plugin. - Always namespace your methods, events and data.