三十六、最好用的懒加载

window.Echo=(function(window,document,undefined){'use strict';var store=[],offset,throttle,poll;var _inView=function(el){var coords=el.getBoundingClientRect();return((coords.top>=0&&coords.left>=0&&coords.top)<=(window.innerHeight||document.documentElement.clientHeight)+parseInt(offset));};var _pollImages=function(){for(var i=store.length;i--;){var self=store[i];if(_inView(self)){self.src=self.getAttribute('data-echo');store.splice(i,1);}}};var _throttle=function(){clearTimeout(poll);poll=setTimeout(_pollImages,throttle);};var init=function(obj){var nodes=document.querySelectorAll('[data-echo]');var opts=obj||{};offset=opts.offset||0;throttle=opts.throttle||250;for(var i=0;i<nodes.length;i++){store.push(nodes[i]);}_throttle();if(document.addEventListener){window.addEventListener('scroll',_throttle,false);}else{window.attachEvent('onscroll',_throttle);}};return{init:init,render:_throttle};})(window,document);

　　echo.min.js

初始化：

Echo.init({
offset:1, //离可视区域多少像素的图片可以被加载
throttle:1 //图片延迟多少毫秒加载
});