TypeScript - Union Types

Union Types allow you to assign more than one type to a variable and as long as it's in the list, it will be accepted

let someValue: string | number;

let someValue: string | number;
someValue = "Hello";
someValue = 42;

// notice how this won't work
//someValue = true;


let basicString: string;
basicString = "foo";
// basicString = null; <-- nope
                           let basicString2: string | null;
                           basicString2=null;
                           let basicString3: string | number;
//basicString3 = null; <-- nope
                           basicString3=42;