jQuery $(this) selector function and limitations

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