function ready(fn) {    var completed = function() {        if ( document.addEventListener ) {            document.removeEventListener( "DOMContentLoaded", completed, false );            window.removeEventListener( "load", completed, false );        } else {            document.detachEvent( "onreadystatechange", completed );            window.detachEvent( "onload", completed );        }        fn();    }    if (document.readyState === ‘completed‘) { // 页面本身已加载结束        fn();    } else if (document.addEventListener) {        document.addEventListener("DOMContentLoaded", completed, false);        window.addEventListener("load", completed, false);    } else {        document.attachEvent("onreadystatechange", completed);        window.attachEvent("load", completed);    }}ready(function() {    console.log(1);});console.log(3);window.onload = function() {    console.log(2);}console.log(4);// 3,4,1,2