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Intermediate 16 min readModule: Module 9: Classes, Decorators & Object-Oriented TS

Access Modifiers & Parameter Properties

Encapsulate class internals with private, protected, readonly, and concise parameter property constructors.

What You Will Learn in This Lesson

  • Compile-time access modifiers (private, protected, public)
  • ECMAScript native private fields (#field)
  • Constructor parameter properties for instant field binding

Introduction & Core Concept

TypeScript extends JavaScript classes with visibility modifiers, abstract classes, and concise constructor parameter initialization.
WHY DOES THIS MATTER IN THE REAL WORLD?

Parameter properties turn 5-line constructor boilerplate into a single elegant line.

Parameter Properties & Private State

typescript
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class BankAccount {
  // Parameter property initializes and assigns fields automatically
  constructor(
    public readonly accountId: string,
    private balance: number
  ) {}
 
  getBalance(): number {
    return this.balance;
  }
}
 
const acc = new BankAccount("ACC-1", 500);
console.log("Account:", acc.accountId, "| Balance: $" + acc.getBalance());

Line-by-Line Technical Breakdown

1Abstract classes define contracts with partial implementation for child subclasses.

Try It Yourself (Interactive Editor)

Modify the code in real-time and click Run to test live browser output and console logs.

Intelligent Code Runner & Live Sandbox[TYPESCRIPT]
TYPESCRIPT SOURCE EDITOR
Interactive Live Code

Industry Best Practices & Professional Standards

  • Use parameter properties to eliminate repetitive constructor assignments.

Lesson Summary & Core Takeaways

  • Classes and access modifiers provide enterprise object-oriented encapsulation.