example_of_type_unions.ts

type User = {
  firstname: string,
  lastname: string
};
type NumberOrStringOrStudent = string | number | User;

let myValue: NumberOrStringOrStudent;
const sampleUser: User = {
  firstname: 'Sippakorn',
  lastname: 'Raksakiart'
};
myValue = sampleUser;
myValue = 12;
myValue = 'HelloWorld';
myValue = true; // Error `Type 'true' is not assignable to type 'NumberOrStringOrStudent'.`