If you'd like to try it, just use this example:

examples/js/console.html

<script>

console.log("Hello World");

</script>

Try!

Apple Mac OSX

Open JavaScript Console of Chrome on Apple Mac OSX

Command-Option-J

Open JavaScript Console of Firefox on Apple Mac OSX

Command-Option-K

Open JavaScript Console of Opera on Apple Mac OSX

Command-Option-I and the click on "Console"

Safari on Apple Mac OSX

1. First enabled the developer tools
2. Safari Preference (or press Command ,)
3. Click on "Advanced" setting
4. Check the box of "Show Develop menu in menu bar"
5. As explained here Then Command-Option-C will open the console.

MS Windows

Open JavaScript Console of Chrome on MS Windows

Ctrl-Shift-J

Open JavaScript Console of Firefox on MS Windows

Ctrl-Shift-K

Open JavaScript Console of Internet Explorer

F12 then click on the "Console" tab.

Ctrl-` (backtick) will open a smaller console.

Linux