Access modifiers are a crucial feature in TypeScript that control the visibility and accessibility of class members. They play a vital role in enforcing encapsulation, a key principle of object-oriented programming.

Types of Access Modifiers

TypeScript provides three main access modifiers:

public: Members are accessible from anywhere (default)
private: Members are only accessible within the same class
protected: Members are accessible within the class and its subclasses

Public Access Modifier

By default, all class members in TypeScript are public. You can explicitly use the public keyword for clarity:


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

    public displayName(): void {
        console.log(this.name);
    }
}

Public members can be accessed from anywhere, including outside the class.

Private Access Modifier

The private modifier restricts access to the containing class. This is useful for hiding internal implementation details:


class BankAccount {
    private balance: number;

    constructor(initialBalance: number) {
        this.balance = initialBalance;
    }

    public deposit(amount: number): void {
        this.balance += amount;
    }

    public getBalance(): number {
        return this.balance;
    }
}

const account = new BankAccount(1000);
account.deposit(500);
console.log(account.getBalance()); // 1500
// console.log(account.balance); // Error: Property 'balance' is private

In this example, balance is private, ensuring it can only be modified through the class methods.

Protected Access Modifier

The protected modifier allows access within the class and its subclasses, facilitating inheritance while maintaining encapsulation:


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 getEmployeeDetails(): string {
        return `${this.name} works in ${this.department}`;
    }
}

const emp = new Employee("John Doe", "IT");
console.log(emp.getEmployeeDetails()); // John Doe works in IT
// console.log(emp.name); // Error: Property 'name' is protected

Here, name is accessible in both Person and Employee classes, but not outside them.

Best Practices

Use private for internal implementation details
Use protected for members that should be accessible in subclasses
Use public for members that need to be accessed from outside the class
Consider using TypeScript Getters and Setters to control access to private properties

Related Concepts

To deepen your understanding of TypeScript's object-oriented features, explore these related topics:

By mastering access modifiers, you'll be able to create more robust and maintainable TypeScript code, leveraging the full power of object-oriented programming principles.