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any / unknown / never / void

class

Special types: any disables type checking; unknown is type-safe any; never for functions that never return; void for no return value.

Syntax

let x: any let y: unknown function fn(): void

Example

javascript

// any — opt out of type checking
let data: any = fetchSomething();
data.foo.bar.baz; // no error (dangerous)

// unknown — must narrow before use
let input: unknown = getUserInput();
if (typeof input === 'string') {
    console.log(input.toUpperCase()); // safe
}

// void — function with no return
function log(msg: string): void {
    console.log(msg);
}

// never — function never returns
function crash(msg: string): never {
    throw new Error(msg);
}

string / number / boolean

interface