ie9 prompts 'console' undefined solution to the problem_javascript skills

The maintained project ran under IE9 without any problems. After adding the code, I found that it could not be fully displayed. After opening the developer tools of IE, it can be displayed completely. I searched for a long time but couldn't find the reason. Later I found that there was an output statement in the console after opening the developer tools. After turning off the developer tools, I found the prompt 'console' is undefined in the status bar. Why did the previous operation have no problem, but the subsequent one does not? I was puzzled, so I added the following code to the code:

Copy the code The code is as follows:

window.console = window.console || (function(){
var c = {}; c.log = c.warn = c.debug = c.info = c.error = c.time = c .dir = c.profile = c.clear = c.exception = c.trace = c.assert = function(){};
return c;
})();

Then the project is ready to run. After searching, I found that it was caused by a problem with the definition of console in IE9.