TypeScript Basics

tsBasics.ts

let id: number = 5;
let company: string = "Eric";
let isBool: boolean = true;
let x: any = 2;
x = false;

let ids: number[] = [1, 2, 3, 4, 5];
let arr: any[] = [1, true, "asf"];

// Tuple (fixed number of elements and types)
let person: [number, string, boolean] = [1, "3", true];

let employee: [number, string][];

employee = [
  [1, "brad"],
  [2, "Eric"],
];

// Union
type Point = number | string;

let pid: string | number = "324";

// Enum
enum Direction1 {
  Up = 1,
  Down,
  Left,
  Right,
}

enum Direction2 {
  Up = "Up",
  Down = "Down",
  Left = "Left",
  Right = "Right",
}

// Objects
type User = { id: number; name: string };

const user: User = {
  id: 1,
  name: "John",
};

// Type Assertion
let cid: any = 1;
// let customerId = <number>cid;
let customerId = cid as number;

// Functions
function addNum(x: number, y: number): number {
  return x + y;
}

function log(message: string | number): void {
  console.log(message);
}

// Interface
interface UserInterface {
  readonly id: number;
  name: string;
  age?: number;
}

const user1: UserInterface = {
  id: 1,
  name: "John",
};

// interface for function
interface Mathfunc {
  (x: number, y: number): number;
}
const add: Mathfunc = (x: number, y: number): number => x + y;
const sub: Mathfunc = (x: number, y: number): number => x - y;

// Classes

interface PersonInterface {
  name: string;
  register(): string;
}

class Person implements PersonInterface {
  private id: number;
  protected pid: number;
  name: string;

  constructor(id: number, pid: number, name: string) {
    this.id = id;
    this.pid = pid;
    this.name = name;
  }

  register() {
    return `ID ${this.id} : ${this.name} is now registered`;
  }
}

const eric = new Person(1, 424, "eric");
const mike = new Person(2, 4354, "Mike");

console.log(eric.register());

// sub-Class
class Employee extends Person {
  position: string;

  constructor(id: number, pid: number, name: string, position: string) {
    super(id, pid, name);
    this.position = position;
  }
}

const emp = new Employee(3, 3244, "shawn", "Dev");
console.log(emp.register());

// Generics
function getArray<T>(items: T[]): T[] {
  return new Array().concat(items);
}

let numArray = getArray<number>([1, 2, 3, 4]);
let strArray = getArray<string>(["brad", "john", "jill"]);

numArray.push(3);