按需加载的模拟

require

function require(name, callback) {        var newJs = document.createElement('script');        // ie        newJs.onreadystatechange = function(){            if(newJs.readyState === 'loaded' || newJs.readyState === 'complete'){                newJs.onreadystatechange = null;                callback && callback();            }        }        // 正常        newJs.onload = function(){            callback && callback();        }        newJs.src = name;        // document.documentElement 特指 head        document.documentElement.firstChild.appendChild(newJs);    }

借鉴学习来自 O'Reilly JavaScript Patterns