有时需要获取图片的尺寸，这需要在图片加载完成以后才可以
1.load 事件
<!DOCTYPE HTML>
<html>
<head>
<meta charset="utf-8">
<title>img - load event</title>
</head>
<body>
<img id="img1" src="">
<p id="p1">loading...</p>
<script type="text/javascript">
img1.onload = function() {
p1.innerHTML = 'loaded'
}
</script>
</body>
</html>
2.readystatechange事件
<!DOCTYPE HTML>
<html>
<head>
<meta charset="utf-8">
<title>img - readystatechange event</title>
</head>
<body>
<img id="img1" src="http://pic1.win4000.com/wallpaper/f/51c3bb99a21ea.jpg">
<p id="p1">loading...</p>
<script type="text/javascript">
img1.onreadystatechange = function() {
if(img1.readyState=="complete"||img1.readyState=="loaded"){
p1.innerHTML = 'readystatechange:loaded'
}
}
</script>
</body>
</html>
3.img的complete属性
<!DOCTYPE HTML>
<html>
<head>
<meta charset="utf-8">
<title>img - complete attribute</title>
</head>
<body>
<img id="img1" src="http://pic1.win4000.com/wallpaper/f/51c3bb99a21ea.jpg">
<p id="p1">loading...</p>
<script type="text/javascript">
function imgLoad(img, callback) {
var timer = setInterval(function() {
if (img.complete) {
callback(img)
clearInterval(timer)
}
}, 50)
}
imgLoad(img1, function() {
p1.innerHTML('加载完毕')
})
</script>
</body>
</html>
