How to trigger checkbox click event even if it's checked through Javascript code?

You can use the jQuery .trigger() method. See http://api.jquery.com/trigger/

E.g.:

$('#foo').trigger('click');

Getting check status

var checked = $("#selectall").is(":checked");

Then for setting

$("input:checkbox").attr("checked",checked);

You can use .change() function too

E.g.:

$('form input[type=checkbox]').change(function() { console.log('hello') });