Question

In my feeble attempt to learn JavaScript, I bought a book which teaches you how to do things in JavaScript, but forgets to mention WHY.

Coming from PHP I am familiar with the typical function syntax:

function name() {return;}

which from what I understand works the same in JS.

Then I decide I want to attempt to use the YUI 3 framework for a small project to continue learning and come across this…YUI Global Object

YUI().use('node', function(Y) {
   Y.Node.get('#demo');
});

As far as I understand this is using the ‘use’ function of the YUI() object, passing ‘node’ to the ‘use’ function….but then what…why is it declaring a function within another function call?

Could someone please explain the syntax being used here?

Also a good reference that explains JavaScript general syntax’s similar to php.net would also be beneficial.
Thanks for your help.

Answer 1

Its an anonymous function. Its considered a callback.

In PHP 4 and early versions of PHP 5 you might see something like this:

PHP

function callback($var){
   ...
}

array_filter( $array, "callback" );

In later versions of PHP 5 you can define them as anonymous functions inline.

So, in JavaScript, the old version would look like this:

JavaScript

function use_callback(Y){
    Y.Node.get('#demo');
}

YUI().use('node', use_callback);

But by defining an inline anonymous function, you can save the extra clutter and defined function:

YUI().use('node', function(Y) {
   Y.Node.get('#demo');
});

Both those functions are equivalent.