Summary: in this tutorial, you will learn about the TypeScript void
type and how to use it as the return type of functions that do not return any value.
Introduction to TypeScript void type
The void
type denotes the absence of having any type at all. Typically, you use the void
type as the return type of functions that do not return a value. For example:
function log(message): void {
console.log(messsage);
}
Code language: JavaScript (javascript)
It is a good practice to add the void
type as the return type of a function or a method that doesn’t return any value. By doing this, you can gain the following benefits:
- Improve clarity of the code: you do not have to read the whole function body to see if it returns anything.
- Ensure type-safe: you will never assign the function with the
void
return type to a variable.
Notice that if you use the void
type for a variable, you can only assign undefined
to that variable. In this case, the void
type is not useful. For example:
let useless: void = undefined;
useless = 1; // error
Code language: JavaScript (javascript)
If the --strictNullChecks
flag is not specified, you can assign the useless
to null
.
useless = null; // OK if --strictNullChecks is not specified
Code language: JavaScript (javascript)
Summary
- Use the
void
type as the return type of functions that do not return any value.