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Within the function you pass to filter(), you can refer to the current element via the
this keyword. To make it into a jQuery object (so you can access and perform jQuery
methods), simply wrap it in the jQuery function:
this; // Regular element object
jQuery(this); // jQuery object
Here are some other filtering examples to spark your imagination:
// Select all DIV elements with a width between 100px and 200px:
jQuery('div').filter(function(){
var width = jQuery(this).width();
return width > 100 && width < 200;
});
// Select all images with a common image extension:
jQuery('img').filter(function(){
return /\.(jpe?g|png|bmp|gif)(\?.+)?$/.test(this.src);
});
// Select all elements that have either 10 or 20 children:
jQuery('*').filter(function(){
var children = jQuery(this).children().length;
return children === 10 || children === 20;
});
Discussion
There will always be several different ways to do something; this is no less true when
selecting elements with jQuery. The key differential is usually going to be speed; some
ways are fast, others are slow. When you use a complicated selector, you should be
thinking about how much processing jQuery has to do in the background. A longer
and more complex selector will take longer to return results. jQuery’s native methods
can sometimes be much faster than using a single selector, plus there’s the added benefit
of readability. Compare these two techniques:
jQuery('div a:not([href^=http://]), p a:not([href^=http://])');
jQuery('div, p').find('a').not('[href^=http://]');
The second technique is shorter and much more readable than the first. Testing in
Firefox (v3) and Safari (v4) reveals that it’s also faster than the first technique.
2.11 Using the Context Parameter
Problem
You’ve heard of the context parameter but have yet to encounter a situation where it’s
useful.
48 | Chapter 2: Selecting Elements with jQuery