typescript union

1type Cow = {
2  name: string;
3  moo: () => void;
4};
5
6type Dog = {
7  name: string;
8  bark: () => void;
9};
10
11type Cat = {
12  name: string;
13  meow: () => void;
14};
15
16// union type
17type Animals = Cow | Dog | Cat;
18  

1let myVar : string | number;        //Variable with union type declaration
2 
3myVar = 100;            //OK
4myVar = 'Lokesh';       //OK
5 
6myVar = true;           //Error - boolean not allowed
7

1let myVar : string | number;    //myVar can store string and number types
2

1Typescript interfaces aren''t being compiled into the js output, and you can not use them at runtime

1// Union Type: function reacts depending on x type (array of string OR string)
2function welcomePeople(x: string[] | string) {
3  if (Array.isArray(x)) {
4    console.log("Hello, " + x.join(" and "));  		// 'x' is 'string[]'
5  } else {										
6    console.log("Welcome lone traveler " + x);		// 'x' is 'string'
7  }
8}