I know what the type 'void' do on typescript.But i faced following code.
function (obj: void){}
I saw same on typescript documentation https://www.typescriptlang.org/docs/handbook/functions.html
What does type "void" as parameter of funсtion?
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typescriptlang.org/docs/handbook/basic-types.htmlwhatamidoingwithmylife– whatamidoingwithmylife2019-01-20 19:19:52 +00:00Commented Jan 20, 2019 at 19:19
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2 Answers
void is useful as a this type, as it promises that you won't use the this parameter.
function f(this: void, ...) {
// Can't use `this` in here.
}
On other parameters, it's... not as useful. If you have --strictNullChecks off, then you can still call the function by passing null or undefined as the void parameter. If you don't, then you can't even call the function, as void is uninhabited.
If you haven't seen this written as a function parameter before, I suggest you read this section (pun entirely intended) of the documentation.
1 Comment
Austaras
you can still call a
(a: void) => void with no parameter or with anyIn short, void is used to denote lack of value. You can think of it as another way to say undefined.
const foo: void = undefined;
When used as the return type, void communicates that the function will not explicitly return anything.
function log(argument: any): void {
console.log(argument);
}
Although in runtime log implicitly does return undefined, TypeScript makes the conceptual distinction between void and undefined.
function log(argument: any): void {
console.log(argument);
}
const foo: undefined = log('Hello'); // Error — "void" is not "undefined"
When used as the this type, void communicates that the this used during a function call will be the default context of execution — the global scope. There are a few cases where it helps. Creating scope-safe constructors is one of them.
