javascript

■ PREFACE
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editor reappear. Note that the keyboard shortcut for toggling to the Console tab is Ctrl+Shift+L
(Command+Shift+L). Table 1 lists vital keyboard shortcuts for Firebug.
Table 1. Firebug Keyboard Shortcuts
Shortcut Description Windows or Linux Mac
Open Firebug F12 F12
Close Firebug F12 F12
Toggle to Console tab Ctrl+Shift+L Command+Shift+L
Run code in command editor Ctrl+Return Command+Return
If you are a fallible typist, inevitably you will mistype a code sample. Consequently, when you click
Run, JavaScript will print an error in the left panel of Firebug. Those are simply JavaScript’s way of
calling you a dummy.
Syntax and reference errors are the most common. JavaScript names those SyntaxError and
ReferenceError, respectively. So, let’s screw up in both ways now to get you off the schneid with errors.
In Firebug, mistype alert as alrt in order to make a reference error, which is to say you mistyped the
name of something:
alrt("Don't Panic");
As Figure 10 displays, JavaScript prints a ReferenceError containing the message "alrt is not
defined":
Figure 10. OopsJavaScript returns a ReferenceError saying "alrt is not defined".