Why return this.each(function()) in jQuery plugins?

Some of the tutorials and开发者_运维技巧 examples I have seen for developing jQuery plugins tend to return

this.each(function () {
    //Plugin code here
});

at the end of the function that instantiates the plugin but I have yet to see any reasoning behind it, it just seems to be a standard that everyone follows. Can anyone enlighten me as to the reasoning behind this practice?

Edit: For clarification my question was not about why to return this, but rather why the plugin should return this.each.

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When you filter elements with a selector ($('.myclass')), it can match more than only one element.
With each, you iterate over all matched elements and your code is applied to all of them.

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jQuery supports "chainable methods", which means that most jQuery functions should return this. .each() returns this, and if you want $('selector').yourPlugin().css(...) to work, you should return this.

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Let me show you two "equivalent" pieces of code that could clarify your question:

With jQuery "each" function:

(function($) {
    $.fn.mangle = function(options) {
        return this.each(function() {
            $(this).append(' - ' + $(this).data('x'));
        });
    };
})(jQuery);

Without jQuery "each" function:

(function($) {
    $.fn.mangle = function(options) {
        var objs = this;
        for (var i=0; i<objs.length; i++) {
            var obj = objs[i];
            $(obj).append(' - ' + $(obj).data('x'));
        };
        return this;
    };
})(jQuery);

So, basically, each function is used to apply some code to all elements contained in this object (as this usually refers to a group of elements returned by a jQuery selector) and return the reference to this (as each function always returns that reference -to allow chaining calls-)

As a side note: The second approach (-for loop-) is faster (notably on old browsers) than former one (-each function-).

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When you write a plugin you are extending the jQuery object, and because the jQuery object is a sequence you return this.each(function () { }); so that your plugin is executed for each item of the sequence.

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In short it allows you to take advantage of chaining, since it returns everything that has been done till now so the next .anyMethod() can act upon the changed/modified elements.

Additionally, take a look at these links they will give you a lot of information on jQuery plugin development.

http://www.webresourcesdepot.com/jquery-plugin-development-10-tutorials-to-get-started/
http://www.learningjquery.com/2007/10/a-plugin-development-pattern
http://snook.ca/archives/javascript/jquery_plugin

And here you have a nice web based app that helps you jump start your jQuery plugins. http://starter.pixelgraphics.us/