JavaScript: How do I print a message to the error console?

Question

How can I print a message to the error console, preferably including a variable? e.g., something like

print('x=%d', x);

Answer 1

Install Firebug and then you can use console.log(...) and console.debug(...), etc (see the docs for more).

Answer 2

If you are using Firebug and need to support IE, Safari or Opera as well, Firebug Lite adds console.log() support to these browsers.

Answer 3

The WebKit Web Inspector also supports FireBug's console API (just a minor addition to Dan's answer above)

Answer 4

One good way to do this that works cross-browser is outlined in http://www.sitepoint.com/blogs/2008/08/22/debugging-javascript-throw-away-your-alerts/

Answer 5

Exceptions are logged into the javascript console. You can use that if you want to keep Firebug disabled.

function log(msg) {
    setTimeout(function() {
        throw new Error(msg);
    }, 0);
}

Usage:

log('Hello World');
log('another message');