jQuery $(this) selector function and limitations

Question

I need help understanding $(this). Is it possible to narrow the focus of "this" within the parentheses or does "this" preclude the use of any other attributes?

For example: I don't understand why this code:

$(this).children("div")

can't be rewritten like this:

$(this + " div")

without having to resort to something like:

$('#'+$(this).attr("id")+ " div")

Also, can you point me to 'this' in the jQuery documentation? It is difficult to use 'this' as a search term for obvious reasons.

Answer 1

Use .find()

$( this ).find( 'div' )

Or use the context parameter to jQuery( selector, context ) (internally, it just calls find anyway...)

$( 'div', this )

Answer 2

this isn't a jQuery "thing", but a basic JavaScript one. It can't be re-written the way you have in examples because it's an object, in particular either a DOM element or a jQuery object (depending on what context you're in). So if you did this:

 $(this + " div")

What you'd really be doing is calling .toString() on this to concatenate the strings, resulting in:

 $("[object Object] div")

....which isn't a valid selector.

As for further reading, I believe this article continues to be one of the best references/resources to learn what this (a context keyword) means.

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Per comment requests, some examples of what this is in various places:

• Event handlers, for example: $("selector").click(function() { alert(this); });
  • this refers to the DOM element the event handler is being triggered on.
• Inside a jQuery plugin, for example: $.fn.myPlugin = function() { alert(this); });
  • this is the jQuery object the plugin was called/chained on, for example: $("selector").myPlugin();, this is that $("selector") jQuery object.
• Inside any generic function, for example: function myFunc() { alert(this); };
  • this is the context you're in, whether it be an object or something else, a few examples:
  • $("selector").click(myFunc); - this is the DOM element, like above
  • $("selector").click(function() { myFunc(); }); - this is the global content, window
  • myFunc.call(whatThisIs, arg1, arg2); - this is whatThisIs
    • See Function.call() and Function.apply() for more info