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Useful Utility Functions in mootools

The new mootools JavaScript framework has quickly impressed me with its design and usefulness. The library was
clearly written to meet real programmers’ needs while working in JavaScript. Just take a look at some of the new
utility functions and methods it provides.

Note: This article covers functions and methods found in the Array.js and Function.js modules of mootools.

A cleaner array iterator

Mootools provides a Prototype-inspired each method that every JavaScript array inherits. Its syntax is a bit
cleaner because it’s based on the Mozilla Array.prototype.forEach method. The mootools each method allows
you to pass in a second parameter as the context in which the function will be called, allowing you to resolve the
this keyword. Accomplishing this in the Prototype library involves binding the function passed to each:

var x = {sum: 0};

for (var i = 0, fixtures = []; i < 500; i++) {

fixtures.each(function(el, i) {
this.sum+= i

// x.sum = 124750

Accomplishing the same thing in mootools is just a small syntax change (the changed line is highlighted):

var x = {sum: 0};

for (var i = 0, fixtures = []; i < 500; i++) {

fixtures.each(function(el, i) {
this.sum+= i
}, x);

// x.sum = 124750

The mootools each method takes the object that will resolve to this inside the loop as the second argument.

Why should you care about this minor syntax change? Because calling bind on a function every time through a loop
is going to add overhead to your code’s performance. I’ve run the previous code in Firebug with a timer and the
results are very telling:

500 elements each with bind: 39ms
500 elements each: 3ms
1000 elements each with bind: 75ms
1000 elements each: 6ms

Not only is the mootools syntax cleaner, but it performs almost 10 times faster than using the bind method. Keep in
mind that these examples all use mootools’ each method. If I’d used the Prototype each the code would have run
even slower, but that issue has already been well-documented.

Prototype each diversion

The reason Prototype’s each loop runs so slowly is that each iteration of the loop has to run through a try/catch
block in order to look for break and continue statements. If you’re using Prototype’s each and you want to break
or continue in the loop, you must use the following syntax:

[1,2,3,4,5,6,7,8,9,10].each(function(el) {
if (el > 7) throw $break;
if (el == 4) throw $continue;

// Will alert "1", "2", "3", "5", "6", "7"

I’m not here to bash Prototype. It’s a great library. But I think it does need to be pointed out that its each method
will run slower than traditional loops because of the design decision to incorporate a workaround for break and
continue statements.

What, you’re not using break and continue statements? They can really help you cut down on loop iterations. There
is no way to use break or continue in an each loop in mootools, so keep that in mind. You’ll have to use the good
old-fashioned for loop for that one.

Running code at time intervals

JavaScript provides the setTimeout and setInterval functions for running code after a delay or at regular intervals.
This comes in very handy for animations, but also for other GUI functions, such as delaying hiding a menu after
navigating away. The native syntax for this can get a little verbose sometimes, so mootools provides some utility
functions as methods of every function. To run code once after a time delay you use the delay method:

(function(){ alert("Sorry I'm late."); }).delay(5000);

This will run the function after a delay of 5 seconds. You can also run code at a regular interval using the periodical

var annoy = (function(){ console.log('Are we there yet?'); }).periodical(5000);

The previous code will run until the window unloads unless we clear the interval returned by periodical. Mootools
provides a $clear function that will clear any time interval passed to it, whether it was created with delay or


Just be sure to assign the periodical function to a variable, or else you won’t be able to clear it! Talk about

The second parameter to delay and periodical is the context object to call the function within, just like the each
method. This can come in handy when using methods of mootools’ objects:

var xhr = new Ajax('url', {update: ajaxElement});
var $req = xhr.request.periodical(60000, xhr);

This code will create an Ajax object that calls its request object every minute. You need to pass the Ajax object as
the second argument to periodical so the request method will run in the right context.

Cleaner object detection

Sometimes checking the type of a JavaScript object can get confusing. Everything is actually an Object, so running
[1,2,3] instanceof Object returns true, even though we were checking against an array. But curisouly, running 'string'
instanceof Object returns false! There’s also the typeof function, so things can get rather confusing and frustrating in
a hurry when trying to detect object types. Mootools provides a function called $type that will do the proper checks
behind the scenes and return a lowercase string type of the element you passed into the function. If the type of
object is not matched, $type will return false.

The types returned by $type are:

  • function
  • textnode
  • element
  • array
  • object
  • string
  • number
  • false

Try it out:

// Returns 'function'

// Returns 'element'

// Returns 'array'

// Returns 'object'

$type('hello world');
// Returns 'string'

// Returns 'number'

Mootools just continues to amaze me. I’m digging through the source code and running lots of tests to see just
how the library works, so stay tuned for more articles about this new library’s features.

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Useful Utility Functions in mootools