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));   }; }()); 

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Modern language features can significantly simplify this snippet:

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