- 3.1 Declaring Functions
- 3.2 Higher-Order Functions
- 3.3 Function Literals
- 3.4 Arrow Functions
- 3.5 Functional Array Processing
- 3.6 Closures
- 3.7 Hard Objects
- 3.8 Strict Mode
- 3.9 Testing Argument Types
- 3.10 Supplying More or Fewer Arguments
- 3.11 Default Arguments
- 3.12 Rest Parameters and the Spread Operator
- 3.13 Simulating Named Arguments with Destructuring
- 3.14 Hoisting
- 3.15 Throwing Exceptions
- 3.16 Catching Exceptions
- 3.17 The finally Clause
- Exercises
This chapter is from the book
This chapter is from the book
This chapter is from the book
3.17 The finally Clause
A try statement can optionally have a finally clause. The code in the finally clause executes whether or not an exception occurred.
Let us first look at the simplest case: a try statement with a finally clause but no catch clause:
try {
// Acquire resources
. . .
// Do work
. . .
} finally {
// Relinquish resources
. . .
}
The finally clause is executed in all of the following cases:
If all statements in the try clause completed without throwing an exception
If a return or break statement was executed in the try clause
If an exception occurred in any of the statements of the try clause
You can also have a try statement with catch and finally clauses:
try {
. . .
} catch (e) {
. . .
} finally {
. . .
}
Now there is an additional pathway. If an exception occurs in the try clause, the catch clause is executed. No matter how the catch clause exits (normally or through a return/break/throw), the finally clause is executed afterwards.
The purpose of the finally clause is to have a single location for relinquishing resources (such as file handles or database connections) that were acquired in the try clause, whether or not an exception occurred.
CAUTION
It is legal, but confusing, to have return/break/throw statements in the finally clause. These statements take precedence over any statements in the try and catch clauses. For example:
try {
// Do work
. . .
return true
} finally {
. . .
return false
}
If the try block is successful and return true is executed, the finally clause follows. Its return false masks the prior return statement.