unions.ts

let u1: number | string | boolean = 1;
console.log(u1);

let u2 = 1 | 2;
console.log(u2);

// The left-hand side of an arithmetic operation must be of type 'any', 'number' or an enum type.
// let u3 = 'A' | 'B';

interface A {
  message: string;
}

interface B {
  message: string;
}

// No error
let u4: A | B = {
  message: "Test"
};
console.log(u4);

// error TS2322: Type '{ error: string; }' is not assignable to type 'A | B'.let u5: A | B = {
error: "Test"
};
console.log(u5);