JQuery在循环中绑定事件的问题详解

<input type="text" name="username" id="username_1" value="" />
<input type="text" name="username" id="username_2" value="" />
<input type="text" name="username" id="username_3" value="" />

$(function(){
 for(var i=1; i<=3; i++){
  $('#username_'+i).onclick(function(){
   alert(i);
  });
 }
});

$(function(){
 for (var i=1; i<=3; i++){
  $("#username_"+i).bind("click", {index: i}, clickHandler);
 }

 function clickHandler(event) {
  var i= event.data.index;
  alert(i);
 }
});