SOURCE

//闭包实现.
for (var i = 0; i < 5; i++) {
var btn = document.createElement('button');
btn.appendChild(document.createTextNode('按钮' + i));
btn.addEventListener('click', (function(i) {
    return function() { alert(i); };
})(i));
document.body.appendChild(btn);
}
//两种方式
for (var i = 0; i < 5; i++) {
var btn = document.createElement('button');
btn.appendChild(document.createTextNode('按钮' + i));
	(function(x){
		btn.addEventListener('click', function() {
				alert(x); 
			})	
	})(i)
document.body.appendChild(btn);
}