Specify Return Type for Functions in TypeScript

We can specify the type of value a function should return using TypeScript.

Inferred Return Type

Here we have a function that accepts two arguments, both are numbers.

function add(num1: number, num2: number) {
  return num1 + num2;
}

Since both num1 and num2 are numbers, TypeScript infers the return type as number. If you try to assign the result of add() to a string variable, we get error.

const a: string = add(2, 3); // Error

Setting Return Type Explicitly

Here is a function that returns a string type explicitly.

function add(num1: number, num2: number): string {
  return "";
}

Specifying return type explicitly, helps TypeScript to point out any errors as early as possible.

A function that does not return anything

If a function does not return anything, the return type is void.

function print(message: string): void {
  // logic...
}