Reducing boilerplat in chaining pattern

const myFunctions = {
  'filter': predicate => function*() {
    for (const item of this) {
      if (predicate(item)) {
        yield item;
      }
    }
  },
  'map': mapper => function*() { /* ... */ }
};

for (const fun of Object.keys(myFunctions)) {
  List.prototype[fun] = function (...args) {
    return new List(myFunctions[fun].apply(this, args));
  };
}