Javascript – Intercept calls to console.log in Chrome

consoledebuggingjavascript

I have a script that I can't change that makes a lot of console.log calls. I want to add another layer and respond if the calls contain certain strings. This works in Firefox, but throws an "Illegal invocation" error in Chrome on the 4th line:

var oldConsole = {};
oldConsole.log = console.log;
console.log = function (arg) {
    oldConsole.log('MY CONSOLE!!');
    oldConsole.log(arg);
}

Any ideas how to get around that? I also tried cloning the console…

Best Answer

You need to call console.log in the context of console for chrome:

(function () {
  var log = console.log;
  console.log = function () {
    log.call(this, 'My Console!!!');
    log.apply(this, Array.prototype.slice.call(arguments));
  };
}());

Modern language features can significantly simplify this snippet:

{
  const log = console.log.bind(console)
  console.log = (...args) => {
    log('My Console!!!')
    log(...args)
  }
}

Related Solutions

Javascript – How to print debug messages in the Google Chrome JavaScript Console

Executing following code from the browser address bar:

javascript: console.log(2);

successfully prints message to the "JavaScript Console" in Google Chrome.

Javascript – How to quickly and conveniently disable all console.log statements in the code

Redefine the console.log function in your script.

console.log = function() {}

That's it, no more messages to console.

EDIT:

Expanding on Cide's idea. A custom logger which you can use to toggle logging on/off from your code.

From my Firefox console:

var logger = function()
{
    var oldConsoleLog = null;
    var pub = {};

    pub.enableLogger =  function enableLogger() 
                        {
                            if(oldConsoleLog == null)
                                return;

                            window['console']['log'] = oldConsoleLog;
                        };

    pub.disableLogger = function disableLogger()
                        {
                            oldConsoleLog = console.log;
                            window['console']['log'] = function() {};
                        };

    return pub;
}();

$(document).ready(
    function()
    {
        console.log('hello');

        logger.disableLogger();
        console.log('hi', 'hiya');
        console.log('this wont show up in console');

        logger.enableLogger();
        console.log('This will show up!');
    }
 );

How to use the above 'logger'? In your ready event, call logger.disableLogger so that console messages are not logged. Add calls to logger.enableLogger and logger.disableLogger inside the method for which you want to log messages to the console.

Best Answer

Related Solutions

Javascript – How to print debug messages in the Google Chrome JavaScript Console

Javascript – How to quickly and conveniently disable all console.log statements in the code

Related Topic