Using the void type

In TypeScript, it is mandatory to define the type of the return of a function. When we have a function that does not have a return, we use a type called void.

Let's see how it works:

Create a new file called void.ts inside the chapter-02 folder, and add the following code:

function myVoidExample(firstName: string, lastName: string): string {
    return firstName + lastName;
}
console.log(myVoidExample('Jhonny ', 'Cash'));

In the preceding code, everything is OK, because our function returns a value. If we remove the return function, we will see the following error message:

void.ts(1,62): error TS2355: A function whose declared type is neither 'void' nor 'any' must return a value.

In VS Code, you would see the following:

To fix it, replace the type string with void:

function myVoidExample(firstName: string, lastName: string): void {
const name = firstName + lastName;
}

This is very useful, because our functions do not always return a value. But remember, we cannot declare void in functions that do return a value.