}
finally
{
console
.
log
(
"...always executed"
);
console
.
log
(
"perform cleanup here"
);
}
Try this example with and without the
throw
statement; you will see that the
finally
block is executed in either case.
Let Exceptions Be Exceptional
Now that you know what exception handling is and how to do it, you might be
tempted to use it for all of your error handling—both the common errors you antici‐
pate, and the errors that you don’t. Throwing an error is, after all, extremely easy, and
it’s a convenient way to “give up” when you encounter a condition that you don’t
know how to handle. But exception handling comes at a cost. In addition to the risk
of the exception never being caught (thereby crashing your program), exceptions
carry a certain computational cost. Because exceptions have to “unwind” the stack
trace until a
catch
block is encountered, the JavaScript interpreter has to do extra
housekeeping. With ever-increasing computer speeds, this becomes less and less of a
concern, but throwing exceptions in frequently used execution paths can cause a per‐
formance issue.
Remember that every time you throw an exception, you have to catch it (unless you
want your program to crash). You can’t get something for nothing. It’s best to leave
exceptions as a last line of defense, for handling the exceptional errors you can’t antic‐
ipate, and to manage anticipated errors with control flow statements.
174 | Chapter 11: Exceptions and Error Handling
