原生js--文档加载时间

 var whenReady = ( function(){
     var funcs = [];
     var ready = false;

     function handler( e ){
         if( ready ) return;
         if( e.type === "readystatechange" && document.readyState !== "complete" ) return;
         for( var i=0; i < funcs.length; i++ ){
             funcs[i].call( document );
         }
         ready = true;
         funcs = null;
     }

     if( document.addEventListener ){
         document.addEventListener( "DOMContentLoaded", handler, false );
         document.addEventListener( "readystatechange", handler, false );
         window.addEventListener( "load", handler, false );
     }else if( document.attachEvent ){
         document.attachEvent( "onreadystatechange", handler );
         window.attachEvent( "load", handler );
     }

     return function whenReady( f ){
         if( ready ) f.call( document );
         else funcs.push( f );
     }
 }() );