The Blueprint
In most javascript frameworks, one of the most powerful tools they offer is the DOM selector function. It’s commonly known in Mootools and Prototype as the double-dollar ($$) and in jQuery it’s just a single-dollar ($). It allows us to search and find elements in the DOM and return them as an array.
For instance, $$(“p”) will return an array of all the elements in the DOM with the p tag. A more powerful example would be $$(“.post”), where you get a returned array of elements that have the class “post”. Add in some Mootools slickness and we can really make it powerful by use of the Selectors such as $$(“.post:last-child”) to select the last element that has the class “post”.
As I’ve been active in the Mootools forums and various blogs and such, I’ve seen lots of people that are new to Mootools (or JS in general), not quite understand what to do with this function. One of the key things to remember when dealing with this function is that it returns the elements in a way that you can apply all the Mootools element methods.
Here are some examples of how I often see this function overcomplicated
//Common way that is used
$$('.status').each(function(el){
el.set('html','Success');
});
//Shorter way to write this
$$('.status').set('html','Success');
Or a more complex example where chaining together methods can be used. As Aaron points out in the comments chaining methods causes the selector to run multiple times, which with a large result set will hinder performance.
//Common way that is used
$$('.status').each(function(el){
el.set('html','Success');
el.highlight();
});
//Shorter way to write this
$$('.status').set('html','Success').highlight();
Mootools also allows you to apply Tween or Morph directly on an element such as element.tween(‘color’, ‘#009900′) or element.morph(‘.class_name’). This allows us to also use tween and morph via the double-dollar($$) like:
//Using Tween to change the text color in last p tag in the DOM
$$('p:last-child').tween('color', '#009900');
//Using Morph to morph all p tags in the DOM to a class named "large"
$$('p').morph('.large');
There are definitely times when we should use the “each” array itterator to do several things to each value, but more often than not I see it overused which really complicated the code. And that has a chain reaction that will further make it harder for new users to understand how to use the framework. Mootools has gone to great lengths to allow us to simplify our code and we should be using this shorter code whenever possible.
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Hi:
I’m one of those JS newbies abusing ‘each’ function.
I’ve found this post very helpful.
Thanks a lot for sharing your wisdom.
It’s a bad practice to chain methods against a selector result. When you do:
$$(selector).method()
MooTools is calling .each and looping through the array of elements. If you chain like this:
$$(selector).method().otherMethod();
MooTools iterates over the array of elements again. This will affect performance of your code, perhaps dramatically if the selector returns a large number of elements. You should only use this shortcut when you are going to call only a single method against the elements.
Ah. Very good point!
I was thinking primarily about small result sets, but not using the chained methods on larger result sets. I’ll note it in the post. Thanks!
nice tutorials, glad i choose mootools as my framework
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