const p1 = new Promise((resolve) => {
  console.log("A");
  resolve("B");
});

const p2 = p1.then((val) => {
  console.log(val);
  return "C";
});

p2.then((val) => {
  console.log(val);
});

console.log("D");

function highlight(strings, ...values) {
  return strings.reduce((result, str, i) => {
    const value = values[i - 1];
    const transformed =
      typeof value === "number"
        ? `[${value * 2}]`
        : `(${String(value).toUpperCase()})`;
    return result + transformed + str;
  });
}

const product = "widget";
const qty = 4;
const price = 12.5;

const output = highlight`Order: ${product} x${qty} @ $${price}`;
console.log(output);

function* pipeline(...fns) {
  let value = yield;
  for (const fn of fns) {
    value = yield fn(value);
  }
  return value;
}

const double  = x => x * 2;
const addTen  = x => x + 10;
const square  = x => x * x;

const gen = pipeline(double, addTen, square);

gen.next();           // prime the generator
const r1 = gen.next(3);
const r2 = gen.next(r1.value);
const r3 = gen.next(r2.value);

console.log(r1.value, r2.value, r3.value);

class Timer {
  constructor() { this.seconds = 0; }
  start() {
    this.tick = () => { this.seconds++; return this.seconds; };
    return this.tick;
  }
}

const t = new Timer();
const tick = t.start();
const obj = { seconds: 100, tick };
console.log(tick(), obj.tick(), t.seconds);

const primArr = [1, 2, 3];
const copyArr = [...primArr];
copyArr[0] = 99;

const objArr = [{ x: 1 }, { x: 2 }];
const copyObjArr = [...objArr];
copyObjArr[0].x = 99;

console.log(primArr[0], copyArr[0], objArr[0].x, copyObjArr[0].x);

const arr = [1, [2, 3], [4, [5, 6]], 7];
const a = arr.flat();
const b = arr.flat(2);
const c = arr.flatMap(x => Array.isArray(x) ? x : [x, x]);
const d = [1, 2, 3].flatMap(x => [[x]]);
console.log(JSON.stringify([a, b, c, d]));

const source = {
  _val: 1,
  get val() { return this._val; }
};
const copy1 = Object.assign({}, source);
source._val = 100;
const copy2 = { ...source };
copy1._val = 999;
console.log(copy1.val, copy2.val, source.val, copy1._val);