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Access Modifiers

Beginner~20 min

Access modifiers control the visibility of class members. TypeScript provides three modifiers: public, private, and protected for proper encapsulation.

TypeScript Access Modifiers

Access Modifiers

Output 
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Default: If no modifier is specified, members are public by default.

Modifier Comparison

Modifier Same Class Child Class Outside
public ✓ ✓ ✓
protected ✓ ✓ ✗
private ✓ ✗ ✗

When to Use Each Modifier

  • public: API methods, properties meant to be accessed externally
  • private: Internal implementation details, sensitive data
  • protected: Properties/methods for inheritance hierarchy

Common Mistakes

1. Making Everything Public

// ✗ Poor encapsulation
class User {
    public password: string;  // Exposed!
    public internalId: number;  // Should be private
}

// ✓ Proper encapsulation
class User {
    private password: string;
    private internalId: number;
    public userName: string;
}

2. Using Private When Protected is Needed

class Animal {
    private makeSound() {}  // ✗ Child can't override
}

class Dog extends Animal {
    makeSound() {}  // Error!
}

// ✓ Use protected for inheritance
class Animal {
    protected makeSound() {}
}
Note: TypeScript access modifiers are compile-time only. They don't exist in JavaScript runtime.

Summary

  • public: Accessible everywhere (default)
  • private: Only within the same class
  • protected: Same class + child classes
  • Use private for sensitive data and internal logic
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