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Backend question · Object-oriented programming › Composition & mixins

What does this print?

class Entity { describe() { return "base"; } }
const Timestamped = (B) => class extends B {
  describe() { return "ts>" + super.describe(); }
};
const Auditable = (B) => class extends B {
  describe() { return "audit>" + super.describe(); }
};
class Invoice extends Timestamped(Auditable(Entity)) {}
console.log(new Invoice().describe());
ts>audit>base

It prints ts>audit>base. The chain is built from the inside out: Auditable(Entity) extends Entity, and Timestamped(...) extends that. So Invoice finds Timestamped's describe first. Its super call goes to Auditable, and then to Entity.

"audit>ts>base" is tempting if you read the mixins as if they were applied left to right. The outermost call is the closest parent, so it runs first.