TYPESCRIPT

union types typescript

/*
TypeScript allows us to use more than one data type for a variable 
or a function parameter. This is called union type.
*/
let code: (string | number);
code = 123;   // OK
code = "ABC"; // OK
code = false; // Compiler Error

let empId: string | number;
empId = 111; // OK
empId = "E111"; // OK
empId = true; // Compiler Error

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;
  

union value typescript

let myVar : string | number;        //Variable with union type declaration
 
myVar = 100;            //OK
myVar = 'Lokesh';       //OK
 
myVar = true;           //Error - boolean not allowed

union value typescript

let myVar : string | number;    //myVar can store string and number types

typescript union

// Union Type: function reacts depending on x type (array of string OR string)
function welcomePeople(x: string[] | string) {
  if (Array.isArray(x)) {
    console.log("Hello, " + x.join(" and "));  		// 'x' is 'string[]'
  } else {										
    console.log("Welcome lone traveler " + x);		// 'x' is 'string'
  }
}