问'控制台'是未定义的？

/**

 * Protect window.console method calls, e.g. console is not defined on IE

 * unless dev tools are open, and IE doesn't define console.debug

 * 

 * Chrome 41.0.2272.118: debug,error,info,log,warn,dir,dirxml,table,trace,assert,count,markTimeline,profile,profileEnd,time,timeEnd,timeStamp,timeline,timelineEnd,group,groupCollapsed,groupEnd,clea

 * Firefox 37.0.1: log,info,warn,error,exception,debug,table,trace,dir,group,groupCollapsed,groupEnd,time,timeEnd,profile,profileEnd,assert,count

 * Internet Explorer 11: select,log,info,warn,error,debug,assert,time,timeEnd,timeStamp,group,groupCollapsed,groupEnd,trace,clear,dir,dirxml,count,countReset,cd

 * Safari 6.2.4: debug,error,log,info,warn,clear,dir,dirxml,table,trace,assert,count,profile,profileEnd,time,timeEnd,timeStamp,group,groupCollapsed,groupEnd

 * Opera 28.0.1750.48: debug,error,info,log,warn,dir,dirxml,table,trace,assert,count,markTimeline,profile,profileEnd,time,timeEnd,timeStamp,timeline,timelineEnd,group,groupCollapsed,groupEnd,clea

 */

(function() {

  // Union of Chrome, Firefox, IE, Opera, and Safari console methods

  var methods = ["assert", "cd", "clear", "count", "countReset",

    "debug", "dir", "dirxml", "error", "exception", "group", "groupCollapsed",

    "groupEnd", "info", "log", "markTimeline", "profile", "profileEnd",

    "select", "table", "time", "timeEnd", "timeStamp", "timeline",

    "timelineEnd", "trace", "warn"];

  var length = methods.length;

  var console = (window.console = window.console || {});

  var method;

  var noop = function() {};

  while (length--) {

    method = methods[length];

    // define undefined methods as noops to prevent errors

    if (!console[method])

      console[method] = noop;

  }

})();

if (!window.console) console = ...

或者if (typeof console === 'undefined') console = ...