Typescript/Class
created : 2020-04-07T11:33:57+00:00
modified : 2022-03-14T17:50:47+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 ${distanceInMeters}m.`);
}
}
class Snake extneds Animal {
constructor(name: string) { super(name); }
move(distanceInMeters = 5) {
console.log("Slithering...");
super.move(distanceInMeters);
}
}
class Horse extends Animal {
constructor(name: string) { super(name); }
move(distanceInMeters = 45) {
console.log("Galloping...");
super.move(distanceInMeters);
}
}
let sam = new Snake("Sammy the Python");
let tom: Animal = new Horse("Tommy the Palomino");
sam.move();
tom.move();
public
, private
and protected
modifiers
Public by default
class Animal {
public name: string;
public constructor(theName: string) { this.name = theName; }
public move (distanceInMeters: number) {
console.log(`${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};