Principles and Applications of image delayed loading and image delayed Loading

Principles and Applications of image delayed loading and image delayed Loading

The basic theory of delayed image loading:
When we browse a page, we sometimes do not read all the content of a page, so when the customer does not browse all the content, loading all images will waste traffic and affect the loading time of webpages. To solve this problem, we designed a mechanism for loading images at a time delay, that is, when users slide pages to images, we start to load images, which saves traffic, and does not affect the user experience.

The following is an example of multiple delayed loading tasks:
First, create the HTML Tag and style required.

    <style type="text/css">        body, div, img {            margin: 0;            padding: 0;        }        img {            border: none;        }        #con {            margin: 10px auto;            padding: 15px 0 15px 15px;            width: 630px;            border: 1px dashed #ff3333;            border-radius: 10px;            overflow: hidden;        }        #con div {            float: left;            margin: 15px 15px 0 0;            width: 300px;            height: 150px;            background: url("img/ddd.jpg") no-repeat;        }        #con div img {            width: 300px;            height: 150px;            opacity: 0;        }    </style>

The overall idea is as follows: First we get the large container for loading images, and then create a div for loading each image so that it occupies a proper position, then, when the user slides to the top of the current div, the image is loaded. After the image is loaded, it is displayed. To prevent the image from being loaded for multiple times, we add an identifier after the image is loaded to prevent the image from being loaded for multiple times.
The code and comments are as follows:

Var date = []; for (var I = 0; I <100; I ++) {var ran = Math. round (Math. random () * 9 + 1); date [date. length] = "img/" + ran + ". jpg ";} // Create the position div; var conBox = document. getElementById ("con"); var frg = document. createDocumentFragment (); for (var I = 0; I <date. length; I ++) {var imgBox = document. createElement ("div"); imgBox. trueSrc = date [I]; frg. appendChild (imgBox);} conBox. appendChild (frg ); // Obtain the height function of the browser getWin (attr) {return document.doc umentElement [attr] | document. body [attr];} // function offset (ele) {var h = ele. offsetTop; var l = ele. offsetLeft; var p = ele. offsetParent; while (p) {if (navigator. userAgent. indexOf ("MSIE 8")>-1) {h + = p. offsetTop; l + = p. offsetLeft;} else {l + = p. offsetLeft + p. clientLeft; h + = p. offsetTop + p. clientTop} p = p. offsetPa Rent ;}return {top: h, left: l };}// function move (oImg) {var n = 0; var timer = window. setInterval (function () {oImg. style. opacity = n; if (n> 0.99) {oImg. style. opacity = 1; clearInterval (timer);} n + = 0.01 ;}, 10)} function loadImg (imgBox) {var oImg = new Image; oImg. src = imgBox. trueSrc; oImg. onload = function () {imgBox. appendChild (oImg); imgBox. loadOk = true; move (oImg );}} // Bind the window function start () {var cur = getWin ("scrollTop") + getWin ("clientHeight"); var imgBox = conBox. getElementsByTagName ("div"); for (var I = 0; I  offset (temp ). top) {if (! Temp. loadOk) {loadImg (temp) ;}}} window. onload = start; window. onscroll = start;

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