js加载前显示loading（页面加载前）

  工作中遇到，需要加loading。1、用jquery的load方法读取页面，页面读取完成前显示loading。2、首页js等加载过慢，页面加载完成前显示loading。        (1).jquery .load()方法，load完成前显示loading                                                                                                                                                                                                                                                                                   $("#menu1").click(function(){                        $('#main_loading').show();                        $('#main-page').load('page_a.html',function () {                                $('#main_loading').hide();                        });                })            2、首页页面加载完成前显示loading                 // 首页加载时loading        document.onreadystatechange = completeLoading;        // 加载状态为complete时移除loading效果        function completeLoading() {                if (document.readyState =="complete") {                        document.getElementById('main_loading').style.display="none";                }                else{                        document.getElementById('main_loading').style.display="block";                }        }