What is the Command pattern and where is it useful in JavaScript apps?

Command encapsulates an action (and its parameters) as an object with a consistent execute() method, so actions can be queued, logged, undone, or passed around independently of the code that triggers them.

class AddItemCommand {
  constructor(cart, item) { this.cart = cart; this.item = item; }
  execute() { this.cart.push(this.item); }
  undo() { this.cart.pop(); }
}