DOMContentLoaded实现

        /**
         * 实现DomContentLoaded的兼容性
         * @param callback
         */
        var onDomContentLoaded = function(callback){
            var onlyOnce = true;
            var onReady = function(callback){
                if(onlyOnce){
                    onlyOnce = false;
                    onDomContentLoaded.isDomReady = true;
                    try{
                        callback();
                    }catch(e){
                        throw(new Error(‘DOM Ready callback occurs an error!‘))
                    }
                }
                return;
            }

            if(S.browser.isIe && !(‘HTMLElement‘ in window)){  // lt IE9
                if(self.top === self){
                    function s(){
                        try{
                            document.documentElement.doScroll(‘left‘);
                            onReady(callback);
                            return;
                        }catch(e){
                            setTimeout(s,50);
                        }
                    }
                    s();
                }else{ //包含框架
                    document.attachEvent(‘onreadystatechange‘,function(){
                        if(document.readyState === ‘complete‘){
                            onReady(callback);
                            document.detachEvent(‘onreadystatechange‘,arguments.callee);
                        }
                    });
                }

                document.onload = function(){
                    onReady(callback);
                    document.onload = null;
                };
            }else{
                document.addEventListener(‘DOMContentLoaded‘,function(){
                    onReady(callback);
                    document.removeEventListener(‘DOMContentLoaded‘,arguments.callee);
                },false);

                document.onload = function(){
                    onReady(callback);
                    document.onload = null;
                };
            }
        };