What is Domain-Driven Design (DDD), and how do its concepts of entities, value objects, and aggregates apply to a Node.js codebase?

Domain-Driven Design structures code around the business domain itself rather than technical layers -- an entity is an object with a distinct identity that persists over time (a User with a stable ID), a value object is defined entirely by its attributes with no identity of its own (an Address or a Money amount, where two instances with identical values are interchangeable), and an aggregate is a cluster of entities and value objects treated as a single consistency boundary, with one designated 'aggregate root' controlling all access and enforcing invariants for the whole cluster.

class Money { // value object: equality is by value, and it's immutable
  constructor(amount, currency) { this.amount = amount; this.currency = currency; Object.freeze(this); }
  equals(other) { return this.amount === other.amount && this.currency === other.currency; }
}

class Order { // entity: has identity, and acts as the aggregate root
  constructor(id) { this.id = id; this.items = []; this.total = new Money(0, 'USD'); }
  addItem(item) { this.items.push(item); this.total = this.recalculateTotal(); }
}