Overview
JQuery offers a very practical and easy way to build plugins, as well as a very good documentation on this subject. However, it could be useful to see how a plugin is written step-by-step.
Basic Structure
The basis of creating a plugin for jQuery is actually quite simple. You don’t have to be a jQuery ninja, nor do you have to sweat blood to make it work. It’s as easy as script writing!
Following the jQuery plugin authoring guidelines is a good idea. Bear in mind that 1) plugins files should be named jquery.PLUGINNAME.js and 2) always attach your plugins to jQuery instead of $, so aliases can be easily set using the noConflict() method.
The structure required to extend the jQuery.fn object is…
jQuery.fn.firstPlugin = function () { return this.each (function () { alert (this.id); }); }
You’d now be able to call your plugin as you normally would call any other plugin
$('#test').firstPlugin ();
This would display a “nice” alert box showing the element id.
One Step Further: Parameters
Ok, I agree the above example was a bit lame, so let’s find out how a more complex plugin can be developed. You can code your plugin to require some parameters and accept other options as well. If your plugin needs two numbers, you could write it in the following way:
jQuery.fn.secondPlugin = function (number1, number2, options) { myoptions = jQuery.extend ({ operation: "sum", label: "The result is" }, options); $(this).html (myoptions.label + " (" + myoptions.operation + ")" + myoptions.number1+myoptions.number2); }
In the above code, check out the way we provide default settings in case the two strings are not passed to the plugin function. This way we can call either
$('#test').secondPlugin (1, 2);
to get
<span id="test The result is (sum) 3</span>or
$('#test').secondPlugin (1, 2, { operation: "sums two numbers together", label: "We got" });
if you prefer
<span id="test We got (sums two numbers together) 3</span>The jQuery Object: Custom Functions and Selectors
Until now, we’ve messed with the jQuery.fn object, which is responsible for elements interaction, and we never mentioned the jQuery object itself, which handles internal processing. By extending it, we are thus allowed to create our own functions and even selectors for others to use! Here’s how new methods can be added:
jQuery.fn.extend ({ myFirstFunction : function () { alert ("first function") }, thisIsTheSecond : function (message) { alert ("2nd: "+ message) } });
and then called without any problems
$.myFirstFunction (); $.thisIsTheSecond ("hello");
In a very similar fashion you can create your own selectors, provided they don’t exist yet.
jQuery.expr[":"].startsWith = function (element, index, tokens) { if (!tokens[3]) return false; return eval ("/^[/s]*" + tokens[3] + "/i").test ($(element).text()); };
As you can see, the function takes three arguments, being: 1) the matched element, 2) the index of the element and 3) an object that contains parse tokens; the first element of the array is the full filter string (including parameters), the second one is the “:”, the third one is the filter name and, finally, the fourth is the parameter.
You should always check whether the parameter has been passed or not, since the filter could stop working in the latter case.
Wrapping It Up
These are some tips to get you started writing your own jQuery plugins. It’s only by diving in that you’ll fully learn all the things you can do.
Sharing is Caring
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August 10, 2009
Great tips, I’ll try my self but I am not really sure how is gonna finish, I am not eh best on Jquery but if I have any problem I will be here, looking for answers.
.-= Luis Lopez´s last blog ..50+ Awesome Photos You Have Never Seen From Bogota – Colombia =-.
August 11, 2009
Hey, thanks for posting this.. I will definitely be looking more into creating my own jquery plugins in the near future
August 11, 2009
Thanks for posting this. Jquery plugins are very interesting. i have to read more about that.
August 14, 2009
Thanks i learned a lot,
August 17, 2009
Fifth! Good stuff here, this is a good primer. I’ll repost after I build a plugin.
October 22, 2009
Hello from Russia!
Can I quote a post in your blog with the link to you?
October 23, 2009
@Polprav – Sure, as long as you link back that would be perfectly fine, thanks for asking.
November 6, 2009
hey, I didn’t know where to contact you but your layout design looked rearranged on firefox and internet explorer. Anyways, i just suscribd to your rss.
November 12, 2009
I was very pleased to find this site. I wanted to thank you for this great read!!
January 17, 2010
I have problem with “this”
When defining a plugin as $.fn.myPlugin
then passing HTML element into it as follows:
$(“#myElementID”).myPlugin
How can I handle the html element? is it by using “this”?
it didn’t work for me.
Thanks
February 2, 2010
@Alaa Al-Hussein . You can achieve this if your method signature looks like this:
(function($){
$.fn. myPlugin= function() {
//Do something here
};
})(jQuery);
And call your plugin method same as before:
$(“#myElementID”).myPlugin();
And let me know if it helped.
Thanks,
Praveen
February 2, 2010
And also make sure that you have linked original JQuery file in the current page