Intro to Typescript
let bar = 'foo'; // -> the type of bar is interpreted as a string
const three = 3; // -> the type of three is interpreted as a number
bar = 42; // -> works just fine
let bar: string = 'foo'; // -> the type of bar is set to string
const three: number = 3; // -> the type of three is set to number
bar = 42; // -> Type '42' is not assignable to type 'string'.
let list: number; // -> list is set to an(empty) array of numbers