JavaScript

function* generator() {
  yield* [1, 2];
  yield* (function* () { yield 3; yield 4; })();
}

const gen = generator();

console.log([...gen]);

const array = [1, 2, 3];
const result = array.map(function(n) {
  return this ? n : 0;
}, false);

console.log(result);

const obj = { a: 1, b: 2 };
const descriptor = Object.getOwnPropertyDescriptor(obj, 'a');

descriptor.value = 3;
Object.defineProperty(obj, 'a', descriptor);

console.log(obj.a);

function test() {
  console.log(arguments.length);
}

test(1, 2, 3);
test.call(null, 1, 2, 3);

const array = [1, 2, 3, 4];
const result = array.reduceRight((acc, val) => acc - val);

console.log(result);

const obj = {
  a: 1,
  b() {
    return new Promise(resolve => {
      setTimeout(() => {
        resolve(this.a);
      }, 100);
    });
  }
};

obj.b().then(console.log);

obj.a = 2;

const array = [1, 2, 3];
const obj = { a: 1, b: 2 };

array.push(obj);
obj.a = 3;

console.log(array[3].a);