What is the Factory pattern, and how does it differ from calling a class constructor directly?

A factory is a function that encapsulates the logic for deciding which class/object to instantiate and how, hiding that complexity from the caller — useful when construction logic is conditional or needs to vary at runtime.

function createShape(type) {
  switch (type) {
    case 'circle': return new Circle();
    case 'square': return new Square();
    default: throw new Error('Unknown shape');
  }
}