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有時需要擷取圖片的尺寸，這需要在圖片載入完成以後才可以，求方法？
一、load事件
複製代碼 代碼如下:
<!DOCTYPE HTML>
<html>
<head>
<meta charset="utf-8">
<title>img - load event</title>
</head>
<body>
<img id="img1" src="http://pic1.xxx.com/wall/f/51c3bb99a21ea.jpg">
<p id="p1">loading...</p>
<script type="text/javascript">
img1.onload = function() {
p1.innerHTML = 'loaded'
}
</script>
</body>
</html>
測試，所有瀏覽器都顯示出了“loaded”，說明所有瀏覽器都支援img的load事件。
二、readystatechange事件
複製代碼 代碼如下:
<!DOCTYPE HTML>
<html>
<head>
<meta charset="utf-8">
<title>img - readystatechange event</title>
</head>
<body>
<img id="img1" src="http://pic1.xxx.com/wall/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>
readyState為complete和loaded則表明圖片已經載入完畢。測試IE6-IE10支援該事件，其它瀏覽器不支援。
三、img的complete屬性
複製代碼 代碼如下:
<!DOCTYPE HTML>
<html>
<head>
<meta charset="utf-8">
<title>img - complete attribute</title>
</head>
<body>
<img id="img1" src="http://pic1.xxx.com/wall/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('載入完畢')
})
</script>
</body>
</html>
輪詢不斷監測img的complete屬性，如果為true則表明圖片已經載入完畢，停止輪詢。該屬性所有瀏覽器都支援。
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