Custom Type Guards की जानकारी

function isString(value: unknown): value is string {
  return typeof value === "string";
}
const val: unknown = "hello";
if (isString(val)) console.log(val.toUpperCase());

interface User {
  id: number;
  name: string;
}
function isUser(value: any): value is User {
  return typeof value?.id === "number" && typeof value?.name === "string";
}
const data: any = { id: 1, name: "Ravi" };
if (isUser(data)) console.log(data.name);

type Shape = { kind: "circle"; radius: number } | { kind: "square"; side: number };
function isCircle(s: Shape): s is { kind: "circle"; radius: number } {
  return s.kind === "circle";
}
const s: Shape = { kind: "circle", radius: 5 };
if (isCircle(s)) console.log(s.radius);

function isOfType<T>(value: unknown, check: (v: unknown) => boolean): value is T {
  return check(value);
}
const val: unknown = 42;
if (isOfType<number>(val, (v) => typeof v === "number")) console.log(val + 1);

const values: (string | null)[] = ["a", null, "b"];
function isString(v: string | null): v is string {
  return v !== null;
}
const strings = values.filter(isString);
console.log(strings);