When using jQuery on(), why use (document) vs. the element itself?

Question

I'd like a jQuery expert in their own words to explain why the $(document) identifier is recommended by others for jQuery's on() statement vs just using an element itself

Example 1: Why is using $(document) here better then Example #2?

$(document).on("click", ".areaCodeList a", function(){
    // do stuff
});

Example 2: Why is using the element this way considering not good practice compared to Example 1?

$(".areaCodeList a").on("click", function(){
    // do stuff
});

Answer 1

Both of those are valid.

The former works for dynamically added elements. You use document because you're delegating events on children of the document object, so events bubble up to the document level. It's also more convenient to select the closest parent you can (and the parent must exist on the page at load).

The latter still works, and is a preferred way to simply bind events to specific elements.

I personally don't recommend delegating through the document object, but rather the closest parent that exists on page load.

Here are the docs for on().

Answer 2

This is not true.

Those two lines do totally two different things.

The first one is a delegate event with the selector of ".areaCodeList a" while the second line is an event attached to the ".areaCodeList a" elements.

A delegate event will fire to every ".areaCodeList a" element although it was in the DOM when that line executed.

Anyway, attaching delegate events to the document isn't recommended at all. as written in the live docs:

Since all .live() events are attached at the document element, events take the longest and slowest possible path before they are handled

Please read the on docs:

Event handlers are bound only to the currently selected elements; they must exist on the page at the time your code makes the call to .on(). To ensure the elements are present and can be selected, perform event binding inside a document ready handler for elements that are in the HTML markup on the page. If new HTML is being injected into the page, select the elements and attach event handlers after the new HTML is placed into the page. Or, use delegated events to attach an event handler, as described next.

Delegated events have the advantage that they can process events from descendant elements that are added to the document at a later time. By picking an element that is guaranteed to be present at the time the delegated event handler is attached, you can use delegated events to avoid the need to frequently attach and remove event handlers. This element could be the container element of a view in a Model-View-Controller design, for example, or document if the event handler wants to monitor all bubbling events in the document. The document element is available in the head of the document before loading any other HTML, so it is safe to attach events there without waiting for the document to be ready.
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