How do I print debug messages in the Google Chrome JavaScript Console?

Question

How do I print debug messages in the Google Chrome JavaScript Console?

Please note that the JavaScript Console is not the same as the JavaScript Debugger; they have

Answer 1

Simple Internet Explorer 7 and below shim that preserves line numbering for other browsers:

/* Console shim */
(function () {
    var f = function () {};
    if (!window.console) {
        window.console = {
            log:f, info:f, warn:f, debug:f, error:f
        };
    }
}());

Answer 2

In addition to Delan Azabani's answer, I like to share my console.js, and I use for the same purpose. I create a noop console using an array of function names, what is in my opinion a very convenient way to do this, and I took care of Internet Explorer, which has a console.log function, but no console.debug:

// Create a noop console object if the browser doesn't provide one...
if (!window.console){
  window.console = {};
}

// Internet Explorer has a console that has a 'log' function, but no 'debug'. To make console.debug work in Internet Explorer,
// We just map the function (extend for info, etc. if needed)
else {
  if (!window.console.debug && typeof window.console.log !== 'undefined') {
    window.console.debug = window.console.log;
  }
}

// ... and create all functions we expect the console to have (taken from Firebug).
var names = ["log", "debug", "info", "warn", "error", "assert", "dir", "dirxml",
    "group", "groupEnd", "time", "timeEnd", "count", "trace", "profile", "profileEnd"];

for (var i = 0; i < names.length; ++i){
  if(!window.console[names[i]]){
    window.console[names[i]] = function() {};
  }
}

Answer 3

You could use console.log() if you have a debugged code in what programming software editor you have and you will see the output mostly likely the best editor for me (Google Chrome). Just press F12 and press the Console tab. You will see the result. Happy coding. :)

Answer 4

Just add a cool feature which a lot of developers miss:

console.log("this is %o, event is %o, host is %s", this, e, location.host);

This is the magical %o dump clickable and deep-browsable content of a JavaScript object. %s was shown just for a record.

Also this is cool too:

console.log("%s", new Error().stack);

Which gives a Java-like stack trace to the point of the new Error() invocation (including path to file and line number!).

Both %o and new Error().stack are available in Chrome and Firefox!

Also for stack traces in Firefox use:

console.trace();

As https://developer.mozilla.org/en-US/docs/Web/API/console says.

Happy hacking!

UPDATE: Some libraries are written by bad people which redefine the console object for their own purposes. To restore the original browser console after loading library, use:

delete console.log;
delete console.warn;
....

See Stack Overflow question Restoring console.log().

Answer 5

Executing following code from the browser address bar:

javascript: console.log(2);

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

Answer 6

Personally I use this, which is similar to tarek11011's:

// Use a less-common namespace than just 'log'
function myLog(msg)
{
    // Attempt to send a message to the console
    try
    {
        console.log(msg);
    }
    // Fail gracefully if it does not exist
    catch(e){}
}

The main point is that it's a good idea to at least have some practice of logging other than just sticking console.log() right into your JavaScript code, because if you forget about it, and it's on a production site, it can potentially break all of the JavaScript code for that page.