javascript - Picking up Changed Checkbox from Programmatic Check/Uncheck -

given:

html

<input id='a' value='bbb' type='checkbox'> <button id='btn'> click change checkbox </button> 

coffeescript

$('#a').change ->     console.log 'asdfasdf'  $('#btn').click ->     document.getelementbyid('a').checked=true     document.getelementbyid('a').checked=false     document.getelementbyid('a').checked=true 

i expected see 3 console output log messages when first pressed button. saw none.

how can modify on change function log message when checked status changes of checkbox?

because changing value or property programmatically doesn't trigger user events , if need event trigger need yourself

$('#btn').click ->     var $a = $('#a')     for(var i=0; i<3; i++){          settimeout(function(){             $a.prop('checked', !$a[0].checked).change();          },i*500)    }