js0014

闭包来做动画的效果

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<!DOCTYPE html>
<html>
<head>
<title>Using a closure in a timer interval callback</title>
<meta charset="utf-8">
<script src="../assert.js"></script>
<link rel="stylesheet" type="text/css" href="../assert.css">
<style>
#box1{
width: 100px;
height: 100px;
position: relative;
margin:5;
color: white;
font-weight: bolder;
background-color:blue;
margin-bottom: 100px;
}
</style>
</head>
<body>
<div id="box1">First Box</div>
<script>
function animateIt(elementId) {
var elem = document.getElementById(elementId);
var tick = 0;
var timer = setInterval(function(){
if (tick < 100) {
elem.style.left = elem.style.top = tick + "px";
tick++;
}
else {
clearInterval(timer);
assert(tick === 100,
"Tick accessed via a closure.");
assert(elem,
"Element also accessed via a closure.");
assert(timer,
"Timer reference also obtained via a closure." );
}
}, 10);
}
animateIt("box1");
</script>
</body>
</html>