What is the Strategy pattern and how does it help avoid large if/else chains?

Strategy defines a family of interchangeable algorithms/behaviors as separate functions or objects, and lets you swap which one is used at runtime, replacing sprawling conditional logic with a simple lookup or injected dependency.

const strategies = {
  card: (amt) => payWithCard(amt),
  paypal: (amt) => payWithPaypal(amt),
};
function pay(method, amount) {
  return strategies[method](amount);
}