typescript distinguish an object type from union type code example

Example 1: typescript union types

type Cow = {
  name: string;
  moo: () => void;
};

type Dog = {
  name: string;
  bark: () => void;
};

type Cat = {
  name: string;
  meow: () => void;
};

// union type
type Animals = Cow | Dog | Cat;

Example 2: custom types in typescript

// simple type
type Websites = 'www.google.com' | 'reddit.com';
let mySite: Websites = 'www.google.com' //pass
//or
let mySite: Website = 'www.yahoo.com' //error
// the above line will show error because Website type will only accept 2 strings either 'www.google.com' or 'reddit.com'.
// another example. 
type Details = { id: number, name: string, age: number };
let student: Details = { id: 803, name: 'Max', age: 13 }; // pass
//or 
let student: Details = { id: 803, name: 'Max', age: 13, address: 'Delhi' } // error
// the above line will show error because 'address' property is not assignable for Details type variables.
//or
let student: Details = { id: 803, name: 'Max', age: '13' }; // error
// the above line will show error because string value can't be assign to the age value, only numbers.