Learning Angular third edition chapter 2 note

 Chapter 2 Introduction to TypeScript

1.

var brand: string = 'Chevrolet';

var message: string = `Today it's a happy day! I just bought a new ${brand} car`;

no more var; use the let keyword wherever possible.

The const keyword is a way to indicate that a variable should never change.

const brand: string[] = ['Chevrolet', 'Ford', 'General Motors'];

The null and undefined literals require special treatment. In a nutshell, they are typed under the any type, 

which makes it possible to assign these literals to any other variable, regardless of its original type.

2. custom types

type Animal = 'Cheetah' | 'Lion';

const animal: Animal = 'Cheetah';

enum Brands { Chevrolet, Cadillac, Ford, Buick, Chrysler, Dodge };

const myCar: Brands = Brands.Cadillac;

3. fat arrow functions

const double = x => x * 2;

const add = (x, y) => x + y;

const addAndDouble = (x, y) => {

    const sum = x + y;

    return sum * 2;

}

4.

Class decorators is executed before the class gets instantiated.