typeguards.parse-person.ts

function parsePerson(value: unknown): Person | null {
  if (
    typeof value === "object" &&
    value &&
    value.hasOwnProperty("name") &&
    value.hasOwnProperty("age") &&
    value.hasOwnProperty("something")
  ) {
    const { name, age, something } = value;
    if (
      typeof name === "string" &&
      typeof age === "number" &&
      typeof something === "string"
    ) {
      // variables now satisfy the Person interface
      return { name, age, something };
    }
  }

  return null;
}