1. Proxying

// Meta-Programming
// Hooking into runtime-level object meta-operations.

let target = {
  foo: 'Welcome, foo',
};
let proxy = new Proxy(target, {
  get(receiver, name) {
    return name in receiver ? receiver[name] : `Hello, ${name}`;
  },
});
proxy.foo === 'Welcome, foo'; // true
proxy.world === 'Hello, world'; // true