In this article, we are going to declare the functions that throw errors in TypeScript. A function can throw an error if the logic is not correct or you can deliberately declare the function that always throws an error. A function can be created with the different return types with the required type of value it returns.

We will create the error functions with two types of return values as discussed below:

Declare using the void type return value

A function whose return type is not defined will automatically return a void type value. This type of function will throw an error if they accidentally return something.

Syntax:

function function_name(): void/empty{}

Example: The below example will show how you can create a function that throws an error with a void type return value.

Output:

This is a function that throws error
Type 'string' is not assignable to type 'void'

Declare using the never type return value

The function with never type return value will never return anything after the function execution.

Syntax:

function function_name(): never {}

Example: The below example will illustrate how to declare error functions with never type return value.

Output:

18
Passed value is greater than 20 
This is a function with never type return value that throws error