Skip to content

Severity: error
Category: access-modifiers
Stage: Stage 1

Description

When a subclass overrides a method or property, it must not make the member less accessible than the base class declaration. Narrowing visibility would violate the Liskov Substitution Principle: code that holds a reference typed as the base class could no longer rely on the member being accessible.

Permitted direction: a subclass may widen access (e.g., protected → public).
Forbidden direction: a subclass may not narrow access (e.g., public → protected, public → private, or protected → private).

Example

// ✗ error
class Shape {
  public area(): number { return 0 }
}

class Circle extends Shape {
  private area(): number { return 3.14 }   // SJS-E015 — narrowed from public to private
}
// ✗ error
class Base {
  protected describe(): string { return "base" }
}

class Child extends Base {
  private describe(): string { return "child" }   // SJS-E015 — narrowed from protected to private
}

Fix

Keep the same (or wider) access modifier on the overriding member:

// ✓ correct — same visibility
class Shape {
  public area(): number { return 0 }
}

class Circle extends Shape {
  public area(): number { return 3.14 }
}
// ✓ correct — widened from protected to public
class Base {
  protected describe(): string { return "base" }
}

class Child extends Base {
  public describe(): string { return "child" }
}

Related codes

  • SJS-E014 — private or protected member not accessible from this scope
  • SJS-E016 — cannot instantiate an abstract class directly
Documentation