jQuery Behaviours

jQuery Behaviours

bind, live, livequery

Richard Paul, Sep 2009

Unobstrusive Javascript

Clean separation of
Data (HTML)
Style (CSS)
Behaviour (Javascript)
...
<form id="myForm" onsubmit="doSomething()">
...
</form>
...
<script type="text/javascript">
$('#myForm').submit(function() { /* do something */ });
</script>

Javascript Events

In Javascript, events bubble up.
<body>
<div>
<button>A button</button>
</div>
</body>

Clicking the button bubbles the event up (button > div > body)

However IE doesn't play nice with form events (select, change,
submit, reset) , they don't bubble (1).

http://www.quirksmode.org/js/events_order.html
(1) http://blogs.sun.com/greimer/entry/event_delegation_for_submit_change

Event Delegation

Event delegation is the practice of letting events bubble up to a
handling node.

$('table').click(function(event) {
r1c1 r1c2 r1c3
alert(event.target.innerHTML);
});
r2c1 r2c2 r2c3

As the target always points to the element the event
happened on, clicking on any cell will result in its contents
being alerted.

Adding new rows

When adding new cells, no extra work is required.
Clicking a new row will bubble up to the table's click handler.

Demo

In practice you would want to check the element is of the
correct type/class etc.

Binding Mechanisms in jQuery

There are a number of ways of binding behaviour in jQuery

bind $('form').bind('submit', function(){})

live $('form').live('submit', function(){})

liveQuery $('form').liveQuery('submit', function(){})

Commonly when using bind you would use the shortcut method:
$('form').submit(function(){})

Comparison Grid

Event
Dynamic IE6 Form Events jQuery Core
Delegation

bind No No Yes Yes

live Yes Yes No Yes

liveQuery Yes No Yes No (plugin)

Facebox Use Case

Facebox uses jQuery's clone method to copy the required
content into its modal dialog.

Any behaviours initialised with bind aren't applied to the
facebox content.

Facebox with jQuery.live

Solution, use jQuery.live to apply behaviours using the event
delegation style.

$('form').live('submit', function() {
// submit form via ajax
return false;
});

Simple!

What about Internet Exploder?

Recall that IE doesn't bubble form events... like submit.

Using jQuery.live doesn't work for IE as the event doesn't
bubble so the handler is never invoked.

http://www.chigarden.com/2007/10/tutorial-making-the-ie-voodoo-doll/

liveQuery

We can't use jQuery.bind as the form is dynamically created (by
facebox's clone call).

Enter liveQuery

This plugin adds the handler directly to the form element.

No event delegation, and it works in IE6!

Demo

liveQuery uses some fancy tricks (async binding etc) to keep
your website performing.

Comments, queries, suggestions or theories?

jQuery Behaviours

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