Arrays, Tuples, Enums, and Classes

Arrays

let numbers: number[] = [1, 2, 3];
let names: Array<string> = ["A", "B", "C"];

Both syntaxes are valid.

Multidimensional Arrays

let matrix: number[][] = [
    [1, 2],
    [3, 4],
];

Tuples

Tuples are fixed-length arrays with fixed order of types.

let user: [string, number] = ["Sahil", 22];

Common use cases:

React hooks return values
helper functions returning multiple values

Enums

enum Status {
    Pending,
    Success,
    Failed,
}

Enums generate JavaScript output at runtime.

Modern alternative:

type Status = "pending" | "success" | "failed";

Classes

class Person {
    name: string;

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

Access Modifiers

class Account {
    public owner: string;
    private balance: number;
    protected accountId: string;

    constructor(owner: string, balance: number, accountId: string) {
        this.owner = owner;
        this.balance = balance;
        this.accountId = accountId;
    }
}

public

Accessible from anywhere.

private

Accessible only inside the same class.

protected

Accessible in class and subclasses.

Static Members

class MathUtil {
    static PI = 3.14159;
}

const value = MathUtil.PI;

Static members belong to the class, not instances.

Abstract Classes and Override

abstract class Animal {
    abstract makeSound(): void;
}

class Dog extends Animal {
    override makeSound(): void {
        console.log("Woof");
    }
}

graph TD A[Abstract Class Animal] --> B[Dog] A --> C[Cat] B --> D[Override makeSound] C --> E[Override makeSound]