Intercept calls to console.log in Chrome

Question

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...

Answer 1

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)
  }
}