I'm learning jQuery by trying to understand other people's code. I ran into this:
jQuery.fn.myFunc = function(options, callback) {
//stuff
jQuery(this)[settings.event](function(e) {
var self = this,
$self = jQuery( this ),
$body = jQuery( "body" );
//etc.
}
//more stuff
}
My understanding is that $ refers to the jQuery object. So why put $ with $self and $body? And is self the same as $self?
$self has little to do with $, which is an alias for jQuery in this case. Some people prefer to put a dollar sign together with the variable to make a distinction between regular vars and jQuery objects.
example:
var self = 'some string';
var $self = 'another string';
These are declared as two different variables. It's like putting underscore before private variables.
A somewhat popular pattern is:
var foo = 'some string';
var $foo = $('.foo');
That way, you know $foo is a cached jQuery object later on in the code.
This is pure JavaScript.
There is nothing special about $. It is just a character that may be used in variable names.
var $ = 1;
var $$ = 2;
alert($ + $$);
jQuery just assigns it's core function to a variable called $. The code you have assigns this to a local variable called self and the results of calling jQuery with this as an argument to a global variable called $self.
It's ugly, dirty, confusing, but $, self and $self are all different variables that happen to have similar names.
No, it certainly is not. It is just another variable name. The $() you're talking about is actually the jQuery core function. The $self is just a variable. You can even rename it to foo if you want, this doesn't change things. The $ (and _) are legal characters in a Javascript identifier.
Why this is done so is often just some code convention or to avoid clashes with reversed keywords. I often use it for $this as follows:
var $this = $(this);
self and $self aren't the same. The former is the object pointed to by "this" and the latter a jQuery object whose "scope" is the object pointed to by "this". Similarly, $body isn't the body DOM element but the jQuery object whose scope is the body element.
The dollarsign as a prefix in the var name is a usage from the concept of the hungarian notation.
