- 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
3.15 Throwing Exceptions
If a function is unable to compute a result, it can throw an exception. Depending on the kind of failure, this can be a better strategy than returning an error value such as NaN or undefined.
Use a throw statement to throw an exception:
throw value
The exception value can be a value of any type, but it is conventional to throw an error object. The Error function produces such an object with a given string describing the reason.
let reason = `Element ${elem} not found`
throw Error(reason)
When the throw statement executes, the function is terminated immediately. No return value is produced, not even undefined. Execution does not continue in the function call but instead in the nearest catch or finally clause, as described in the following sections.
TIP
Exception handling is a good mechanism for unpredictable situations that the caller might not be able to handle. It is not so suitable for situations where failure is expected. Consider parsing user input. It is exceedingly likely that some users provide unsuitable input. In JavaScript, it is easy to return a “bottom” value such as undefined, null, or NaN (provided, of course, those could not be valid inputs). Or you can return an object that describes success or failure. For example, in Chapter 9, you will see a method that yields objects of the form { status: 'fulfilled', value: result } or { status: 'rejected', reason: exception }.