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Sacrificial Lambda

Dynamically binding event handlers to content that has been ajaxed in with $.load without repeating yourself can be tricky. Lambda functions help you to not repeat yourself as much. jQuery uses lamdba functions everywhere, so if you're familiar with jQuery, you should be familiar with the syntax of lambda functions.

In this example, the ajaxed-in content contains the elements that trigger a $.load over themselves.

JavaScript:
  1. prepare_links = function() {  
  2.   var month = $('.calendar-info .month').html();  
  3.   var year = $('.calendar-info .year').html();    
  4.   $('.previous-month').click(function() {
  5.      $('#calendar').load(this.href, prepare_links);
  6.      return false;
  7.   });
  8.   $('.next-month').click(function() {
  9.      $('#calendar').load(this.href, prepare_links);
  10.      return false;
  11.   });
  12. };
  13. $(document).ready(function() {
  14.    prepare_links();
  15. });

Make sure you're not calling the function in the callback by accidentally using prepare_links():

JavaScript:
  1. $('.next-month').click(function() {
  2.    $('#calendar').load(this.href, prepare_links()); /* Don't do this */
  3.    return false;
  4. });

This would set the callback to whatever the return value of the function is, not to the function itself.

Introducing $(document).ready()

This is the first thing to learn about jQuery: If you want an event to work on your page, you should call it inside the $(document).ready() function. Everything inside it will load as soon as the DOM is loaded and before the page contents are loaded.

Read the rest of this entry »

A Getting Started Guide

Jörn Zaefferer has put together a nice "Getting Started Guide" that can help people, um, get started wtih jQuery. It'll help anyone who is new to jQuery, and even those who are fairly new to JavaScript and programming in general — just the kind of help I like. Here is what the guide includes:

  1. Setup
  2. Hello jQuery
  3. Find me: Using selectors and events
  4. Rate me: Using AJAX
  5. Animate me: Using FX
  6. Sort me: Using tablesorter plugin
  7. Plug me: Writing your own plugins
  8. Next steps
We'll be covering some of these topics here, too, but the more people who get the message out about how easy it is to use jQuery, the better.

Multiple $(document).ready()

One more great thing about $(document).ready() that I didn't mention in my previous post is that you can use it more than once. In fact, if you don't care at all about keeping your code small, you could litter your javascript file with them.

It's great to be able to group your functions within a file or even across multiple files, and jQuery's flexible $(document).ready() function allows you to do that, pain free.

You could, for example, have one .js file that is loaded on every page, and another one that is loaded only on the homepage, both of which would call $(document).ready(). So, inside the <head> tag of your homepage, you would have three references to JavaScript files altogether, like so:

HTML:
  1. <script src="/js/jquery.js" type="text/javascript"></script>
  2. <script src="/js/common.js" type="text/javascript"></script>
  3. <script src="/js/homepage.js" type="text/javascript"></script>

You could also do something like this inside a single .js file:

JavaScript:
  1. $(document).ready(function() {
  2.   // some code here
  3. });
  4. $(document).ready(function() {
  5.   // other code here
  6. });

A final note: In a comment to my previous post, Jörn gave this excellent tip for shrinking your code:

Even for this little amount of code is a shortcut available:

$(function() {
// do something on document ready
});
A function passed as an argument to the jQuery constructor is bound to the document ready event.

Coming Up: In my next entry, I'll show how to do a simple effect with jQuery. You'll be amazed at how easy it is!

Basic Show and Hide

As promised in my last entry, I'll be showing you a simple effect that you can do using jQuery: showing or hiding something, or a group of things, on the page. The two functions that let us do this are, not surprisingly, show() and hide().

jQuery also comes with another function called toggle(), which will make matching elements visible if they are hidden or hidden if they are visible.

So, let's get down to business. We're going to start with our $(document).ready() function.

Read the rest of this entry »

Slicker Show and Hide

Last time I showed you how to make something appear and disappear on a web page. This time I'll show you how to do it with style.

Like we did last time, we'll start with our $(document).ready() and put everything else inside of it.

Adjust the Speed

This time, however, we're going to adjust the speed at which our item shows and hides. To do so, we put a speed indicator — "slow" or "normal" or "fast" or a number of milliseconds (1000 = 1 second) — inside the parentheses: Read the rest of this entry »