實現這個效果，需要引用jQuery以及一個叫做iPass.packed的js外掛。

<div class="loginBox">
    <input id="demo2" name="demo2" type="password" value="" />
    <button>show password</button>
</div>

<script src="http://apps.bdimg.com/libs/jquery/1.8.3/jquery.min.js" charset="utf-8"></script>  
<script type="text/javascript" src="js/iPass.packed.js"></script>
<script type="text/javascript">
$(document).ready(function(){	
	// to enable iPass plugin
	$("input[type=password]").iPass();
	
	// for the demo
	$("button").click(function() {
		alert("Password: "+$("#demo2").val());
	})
});
</script>