Dev : Tips : Printing to JSConsole

You can output information to console using the following method:

• Declare global variable aConsoleService:

var aConsoleService;

• Initialize it on load:

aConsoleService = Components.classes['@mozilla.org/consoleservice;1'].getService(Components.interfaces.nsIConsoleService);

(note, you can also use toJavaScriptConsole() function to open JavaScript console on startup)

• Define a function:

function logMessage(message) {
  aConsoleService.logStringMessage('MyApp: ' + message);
}

• Use it like here:

logMessage('Initialized.');

(thanks to clav, velcrospud and sage.mozdev.org for this)

See also: Using dump()