Typescript/Class

created : 2020-04-07T11:33:57+00:00
modified : 2020-04-08T03:54:30+00:00

Class

class Greeter {
	greeting: string;
	constructor(message: string) {
		this.greeting = message;
	}
	greet() {
		return "Hello, " + this.greeting;
	}
}

let greeter = new Greeter("world");

Inheritance

class Animal {
	move(distanceInMeters: number = 0) {
		console.log(`Animal moved ${distanceInMeters}m.`);
	}
}

class Dog extends Animal {
	bark() {
		console.log("Woof! Woof!");
	}
}

const dog = new Dog();
dog.bark();
dog.move(10);
dog.bark();

class Animal {
	name: string;
	constructor(theName: string) { this.name = theName; }
	move(distanceInMeters: number = 0) {
		console.log(`${this.name} moved ${distanceInMeters}m.`);
	}
}

class Snake extneds Animal {
	constructor(name: string) { super(name); }
	move(distanceInMeters = 5) {
		console.log("Slithering...");
		super.move(distanceInMeters);
	}
}

class Horse extends Animal {
	constructor(name: string) { super(name); }
	move(distanceInMeters = 45) {
		console.log("Galloping...");
		super.move(distanceInMeters);
	}
}

let sam = new Snake("Sammy the Python");
let tom: Animal = new Horse("Tommy the Palomino");

sam.move();
tom.move();

public, privateand protected modifiers

Public by default

class Animal {
	public name: string;
	public constructor(theName: string) { this.name = theName; }
	public move (distanceInMeters: number) {
		console.log(`${this.name} moved ${distanceInMeters}m.`);
	}
}

Understanding private

class Animal {
	private name: string;
	constructor(theName: string_ { this.name = theName; }
}

new Animal("Cat").name; // Error name is private.

class Animal {
	private name: string;
	constructor(theName: string) { this.name = theName; }
}

class Rhino extends Animal {
	constructor() { super("Rhino"); }
}

class Employee {
	private name: string;
	constructor(theName: string) { this.name = theName; }
}

let animal = new Animal("Goat");
let rhino = new Rhino();
let employee = new Employee("Bob");

animal = rhino;
animal = employee; // Error

Understanding protected

class Person {
	protected name: string;
	constructor(name: string) { this.name = name; }
}

class Employee extends Person {
	private department: string;

	constructor(name: string, department: string) {
		super(name);
		this.department = department;
	}

	public getElevatorPitch() {
		return `Hello, my name is ${this.name} and I work in ${this.department}.`;
}
}

let howard = new Employee("Howard", "Sales");
console.log(howard.getElevatorPitch());
console.log(howard.name); // Error

class Person {
	protected name: string;
	protected constructor(theName: string) { this.name = theName; }
}

class Employee extends Person {
	private department: string;

	constructor(name: string, department: string) {
		super(name);
		this.department = department;
	}

	public getELevatorPitch() {
		return `Hello, my name is ${this.name} and I work in ${this.department}.`;
	}
}

let howard = new Employee("Howard", "Sales");
let john = new Person("John");

Readonly modifier

class Octopus {
	readonly name: string;
	readonly numberOfLegs: number = 8;
	constructor (theName: string) {
		this.name = theName;
	}
}

let dad = new Octopus("Man with the 8 strong legs");
dad.name = "Man with the 3-piece suit"; // Error

Parameter properties

class Octopus {
	readonly numberOfLegs: number = 8;
	constructor(readonly name: string) {
	}
}

Accessors

class Employee {
	fullName: string;
}

let employee = new Employee();
employee.fullName = "Bob Smith";
if (employee.fullName) {
	console.log(employee.fullName);
}

let passcode = "secret passcode";

class Employee {
	private _fullName: string;

	get fullName(): string {
		return this._fullName;
	}

	set fullName(newName: string) {
		if (passcode && passcode == "secret passcode") {
			this._fullName = newName;
		}
		else {
			console.log("Error!");
		}
	}
}

let employee = new Employee();
employee.fullName = "Bob Smith";
if (employee.fullName) {
		console.log(employee.fullName);
}

Static Properties

class Grid {
	static origin = { x: 0, y: 0 };
	calculateDistanceFromOrigin(point: { x: number; y: number; }) {
		let xDist = (point.x - Grid.origin.x);
		let yDist = (point.y - Grid.origin.y);
		return Math.sqrt(xDist * xDist + yDist * yDist) / this.scale;
	}
	constructor (public scale: number) { }
}

let grid1 = new Grid(1.0);
let grid2 = new Grid(5.0);

console.log(grid1.calculateDistanceFromOrigin({x: 10, y: 10}));
console.log(grid2.calculateDistanceFromOrigin({x: 10, y: 10}));

Abstacrt Classes

abstract class Animal {
	abstract makeSound(): void;
	move(): void {
		console.log("roaming the earth...");
	}
}

abstract class Department {
	constructor(public name: string) {
	}
	printName(): void {
		console.log("Department name: " + this.name);
	}
	abstract printMeeting(): void;
}

class AccountingDepartment extends Department {
	constructor() {
		super("Accounting and Auditing");
	}
	printMeeting(): void {
		console.log("The Accounting Department meets each Monday at 10am.");
	}
	grenerateReports(): void {
		console.log("Generating accounting reports...");
	}
}

let department: Department;
department = new Department();
department = new AccountingDepartment();

Advanced Techinques

Constructor functions

class Greeter {
	greeting: string;
	constructor(message: string) {
		this.greeting = message;
	}
	greet() {
		return "Hello, " + this.greeting;
	}
}

let greeter: Greeter;
gretter = new Greeter("World");
console.log(greeter.greet());

class Greeter {
	static standardGreeting = "Hello, there";
	greeting:string;
	greet() {
		if (this.greeting) {
			return "Hello, " + this.greeting;
		}
		else {
			return Greeter.standardGreeting;
		}
	}
}

let greeter1: Greeter;
greeter1 = new Greeter();
console.log(greeter1.greet());

let greeterMarker: typeof Greeter = Greeter;
greeterMaker.standardGreeting = "Hey there!";

let greeter2: Greeter = new greeterMaker();
console.log(greeter2.greet());

Using a class as an interface

class Point {
	x: number;
	y: number;
}

interface Point3d extends Point {
	z: number;
}

let point3d: Point3d = {x: 1, y:2, z: 3};