TypeScript void Type

Introduction

In this chapter, we will explore the void type in TypeScript. The void type is typically used to indicate that a function does not return a value. Understanding how to use the void type is essential for correctly defining function return types in your TypeScript programs.

Table of Contents

• Definition
• Using the void Type
• Functions with void Return Type
• Variables of Type void
• Complete Example with Output
• Conclusion

Definition

The void type in TypeScript is used to represent the absence of a value. It is most commonly used as the return type of functions that do not return a value. When a function is specified to return void, it means the function doesn't return any value.

Using the void Type

The void type is primarily used to indicate that a function does not return a value. It can also be used with variables, though this is less common and not very useful in most cases.

Functions with void Return Type

When a function does not return a value, you should specify the return type as void. This makes it clear that the function is intended to perform some actions without producing a result.

Example

function logMessage(message: string): void {
  console.log(message);
}

logMessage("Hello, TypeScript!"); // Output: Hello, TypeScript!

Output

Hello, TypeScript!

Variables of Type void

Declaring variables of type void is not very useful and is generally discouraged, as void means the absence of any value. However, it can be done for specific use cases, such as function parameters that should not be used.

Example

let unusable: void;
unusable = undefined; // The only values you can assign to a variable of type `void` are `undefined` or `null` (if `--strictNullChecks` is not enabled)
console.log(unusable); // Output: undefined

Output

undefined

Complete Example with Output

In this section, we will combine all the examples into a single TypeScript file, compile it to JavaScript, and run it to see the output.

TypeScript Code

You can test the following code in the TypeScript Playground:

// Functions with `void` Return Type
function logMessage(message: string): void {
  console.log(message);
}

logMessage("Hello, TypeScript!"); // Output: Hello, TypeScript!

// Variables of Type `void`
let unusable: void;
unusable = undefined; // The only values you can assign to a variable of type `void` are `undefined` or `null` (if `--strictNullChecks` is not enabled)
console.log(unusable); // Output: undefined

Conclusion

In this chapter, we covered the void type in TypeScript, including how to use it to indicate that a function does not return a value, and how to declare variables of type void. We provided a complete example with its output to illustrate how the void type works in TypeScript. Understanding the void type is essential for correctly defining function return types in your TypeScript programs.