Replace Constructor with Factory Function

Goal

Object creation goes through a named function that can validate, choose subclasses, or return cached instances.

Before the refactoring

const employee = new Employee(name, 'engineer', salary);

After the refactoring

function createEngineer(name, salary) {
  return new Employee(name, 'engineer', salary);
}
const employee = createEngineer(name, salary);

Savings

Construction can vary per case; consumers don't depend on which concrete class they're getting.

Note

Hides the actual class from callers — make sure your factory's name still expresses the produced shape clearly.