one of why hate javascript

gistfile1.js

var buttons = document.querySelectorAll('button');

// fool
for (var i = 0, l = buttons.length; i < l; i++){
	buttons[i].onclick = function(){
		alert(i); // always alert buttons length. not inclemental.
	};
}

// should
for (var i = 0, l = buttons.length; i < l; i++){
	buttons[i].onclick = (function(n){
		var m = n; // create new scope
		return function(){
			alert(m); // inclemental.
		}
	})(i);
}

// Do you not believe yet ? Try run this code, and click any link
var a = document.querySelectorAll('a');
for (var i=0,l=a.length; i<l; i++){
    a[i].onclick=function(){
        alert(i);
    };
}