@studnicky/v8/conditional-property-assignment

V8 assigns an object a hidden class based on the shape (set and order of properties) established during construction. When a constructor assigns this.x only inside an if branch, instances that take different branches end up with different hidden classes, forcing every call site that touches the instance into megamorphic (or at best polymorphic) property access instead of a fast monomorphic one. Assign every property unconditionally in the constructor — compute the conditional value first, then assign it once.

Fixable: No · Options: No · Suggested severity: error

✗ Incorrect

class CircuitBreaker {
  #successThreshold: number;

  constructor(options: CircuitBreakerOptionsInterface) {
    if (options.successThreshold !== undefined) {
      this.#successThreshold = options.successThreshold;
    }
  }
}

✓ Correct

class CircuitBreaker {
  #successThreshold: number;

  constructor(options: CircuitBreakerOptionsInterface) {
    this.#successThreshold = options.successThreshold ?? 1;
  }
}