<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>高阶函数 - 惰性加载函数</title> </head> <body> <div style="width: 100px; height: 100px; background: #f60;" id="div1"></div> <script> /** * 根据作用域链内部会重写外部的addEvent变量(如果在1. 2.处, 在addEvent前加上var就不是惰性了) */ var addEvent = function(ele, type, handler) { if (window.addEventListener) { // 标准 addEvent = function(ele, type, handler) { // 1. ele.addEventListener(type, handler, false); }; } else if (window.attachEvent) { addEvent = function(ele, type, handler) { // 2. ele.attachEvent('on' + type, handler); }; }; addEvent(ele, type, handler); }; var div = document.querySelector('#div1'); addEvent(div, 'click', function() { console.log(111); }); addEvent(div, 'click', function() { console.log(222); }) </script> </body> </html>