Access Modifiers: public, private, protected

Syntax

public prop: type;
private prop: type;
protected prop: type;

Examples

class BankAccount {
  public accountHolder: string;
  private balance: number;
  protected accountNumber: string;

  constructor(holder: string, initialBalance: number, accountNumber: string) {
    this.accountHolder = holder;
    this.balance = initialBalance;
    this.accountNumber = accountNumber;
  }

  public getBalance(): number {
    return this.balance; // accessing private balance is fine from WITHIN the class
  }
}

const account = new BankAccount("Alice", 1000, "ACC-001");
console.log(account.accountHolder); // OK - public
// console.log(account.balance);      // Error - private

class SavingsAccount extends BankAccount {
  showAccountNumber(): string {
    return this.accountNumber; // OK - protected is accessible in subclasses
    // return this.balance;    // Error - private is NOT accessible, even in a subclass
  }
}

Best practices

• Default to private for internal implementation details, exposing only what genuinely needs to be part of the class's public API
• Use protected specifically when subclasses legitimately need access to a member that outside code should not have
• Remember these modifiers are compile-time only - they are erased when compiled to JavaScript and offer no runtime protection, unlike the # private field syntax
• Use JavaScript's native #privateField syntax instead of the private keyword when you need genuine runtime privacy, not just compile-time checking

At a glance

Purpose

Static types for JavaScript

File extension

.ts · .tsx

Runs in

Compiled to JavaScript

Usually used with

JavaScript and its ecosystem

Specifications & further reading

• TypeScript Handbook

Related TypeScript documentation