disable other checkboxes if 3 checkboxes are checked

[al3bed]

hello

im newbie here im not good in javascript but i need this code
i want a function check if 3 checkboxes are checked
and if they checked then it's will disable other checkboxes!

as i say im not good in javascript.. this is my try:

function check_disable(box) {
	
	var index = 0;
	
	for(var i=0;i<box.form.elements.length;i++)
	{
		if(box.form.elements[i].checked == true)
		{index = index + 1;}
		else if(box.form.elements[i].checked == false)
		{index = index - 1;}
	}
	
	if(index >= 3)
	{
		for(i=0;i<box.form.elements.length;i++)
		{
				box.form.elements[i].disabled = !box.checked;
		}
	}
}
-->
</script>

i put onclick="check_disable(this);" in each checkbox
this not work

any help please
thanks

[al3bed]

i found the answer

solved