php如何實現圖片延時載入

php實現圖片延時載入的方法：在到達指定載入圖片位置時，用data-src屬性值替換img的src屬性值即可，如【imgs[i].src = imgs[i].getAttribute('data-src');】。

在到達指定載入圖片位置時，用data-src的屬性值替換img的src的屬性值即可，這個時候img就會去請求資源。

（推薦教學：）

imgs[i].src = imgs[i].getAttribute('data-src');

程式碼實現：

<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>圖片懶載入</title>
    <style>
        img {
            display: block;
            width: 100%;
            height: 300px;
            margin-bottom: 20px;
        }
    </style>
</head>
<body>
    <img data-src="./images/1.jpg" alt="">
    <img data-src="./images/2.jpg" alt="">
    <img data-src="./images/3.jpg" alt="">
    <img data-src="./images/4.jpg" alt="">
    <img data-src="./images/5.jpg" alt="">
    <img data-src="./images/6.jpg" alt="">
    <img data-src="./images/7.jpg" alt="">
    <img data-src="./images/8.jpg" alt="">
    <img data-src="./images/9.jpg" alt="">
    <img data-src="./images/10.jpg" alt="">
    <img data-src="./images/1.jpg" alt="">
    <img data-src="./images/2.jpg" alt="">
</body>
<script>
        var imgs = document.querySelectorAll('img');

        //offsetTop是元素與offsetParent的距離，迴圈獲取直到頁面頂部
        function getTop(e) {
            var T = e.offsetTop;
            while(e = e.offsetParent) {
                T += e.offsetTop;
            }
            return T;
        }

        function lazyLoad(imgs) {
            var H = document.documentElement.clientHeight;//獲取可視區域高度
            var S = document.documentElement.scrollTop || document.body.scrollTop;
            for (var i = 0; i < imgs.length; i++) {
                if (H + S > getTop(imgs[i])) {
                    imgs[i].src = imgs[i].getAttribute('data-src');
                }
            }
        }

        window.onload = window.onscroll = function () { //onscroll()在卷軸捲動的時候觸發
            lazyLoad(imgs);
        }
</script>
</html>