Describe Unions and Intersection Types

In TypeScript, union types and intersection types are ways to specify multiple types for a single value.

A union type represents a value that can be of one of several types. Union types are denoted using the | character, and they allow you to specify that a value can be of multiple types. For example:

let x: string | number;

x = 'hello';  // valid
x = 42;       // valid
x = true;     // invalid

In this example, the x variable is declared as a union type of string and number, which means that it can hold a value of either type. The value of x can be set to a string or a number, but not to a boolean or any other type.

An intersection type represents a value that is of multiple types. Intersection types are denoted using the & character, and they allow you to specify that a value must be of multiple types. For example:

type User = {
  name: string;
  age: number;
};

type Admin = {
  role: string;
};

type SuperUser = User & Admin;

const user: SuperUser = {
  name: 'John',
  age: 42,
  role: 'admin'
};

In this example, the User and Admin types are defined, and they represent objects with different properties. The SuperUser type is defined as an intersection of User and Admin, which means that it represents an object that must have both the name and age properties of the User type, and the role property of the Admin type.