When and where to use unkown ? #

intro #

For the few cases where you have a value whose type you really don’t know ahead of time, don’t use any, and instead reach for unknown. Like any, it represents any value, but TypeScript won’t let you use an unknown type until you refine it by checking what it is

Example #

let a: unknown = 30 // 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
}

TypeScript will never infer something as unknown—you have to explicitly annotate it. You can compare values to values that are of type unknown. But, you can’t do things that assume an unknown value is of a specific type (c); you have to prove to TypeScript that the value really is of that type first (d).

Dealing with big objects like and api response is set to unkown #

How can we deal with it??

const bigObject: unknown = {
  name: "Anshik",
  age: 24,
  details: {
    address: "Delhi",
    phone: "123456",
  },
};

if (
  typeof bigObject === "object" &&
  bigObject !== null &&
  "name" in bigObject
) {
  // to access name file
  const name = (bigObject as any).name;

  // now to access phone field
  if (
    typeof data === "object" &&
    data !== null &&
    "details" in data &&
    typeof (data as any).details === "object" &&
    (data as any).details !== null &&
    "phone" in (data as any).details
  ) {
    const phone = (data as any).details.phone;
    console.log(phone); // "123456"
  }
}