Type unknown in Typescript

Like any, unknown represents any value, but we can’t operate on unknown type until we refine it by checking what it is with typeof or instanceof.

Like boolean, unknown only supports comparison operations(==, ===, ||, &&, ?) and negation operation(!).

let a: unknown = 10;  //unknown
let b = a === 123;  // boolean
let c = a + 10; // Error TS2571: Object is of type 'unknown'
if (typeof a === 'number') {
	let d = a + 10;  // number
}

1. Typescript will never infer something as unknown, we have to explicitly annotate it (a).
2. unknown supports comparison operations and negation operation, same as boolean does(b).
3. we can’t do things that assume an unknown value is of a specific type(c).
4. We can operate on unknown type after checking it with typeof or instanceof.