Q:

How to select a checkbox jquery object

Why my jquery object didn't get checked with $('.checkall').checked = true ;
Here's a Fiddle.
UPDATE : working code

A:

This is a problem of mixing jQuery, and DOM, methods. jQuery doesn't have access to the .value property of the node, instead use:
$('.checkall').prop('checked',true);

Reference:

prop().

A:

Use .prop()
$('.checkall').prop('checked',true)

A:

You need this:
$('.checkall').prop('checked',true);

Or:
$('.checkall')[0].checked = true ;

You would use .prop() to set the property of checked or directly covnert the jQuery element to HTMLElement and then directly set the value. 

