infinity+takeWhile.js

function f1(max) {
  let i = -1, total = 0;
  while (true) {
    let a = ++i;
    a = a * a;
    if (!(a < max)) break;
    total += a;
  }
  return total;
}

log(f1(10), f1(20), f1(30)); // 14 30 55

const f2 = max =>
  reduce((a, b) => a + b,
    takeWhile(a => a < max,
      map(a => a * a,
        infinity())));

log(f2(10), f2(20), f2(30)); // 14 30 55

function *infinity(i = 0) {
  while (true) yield i++;
}

function *takeWhile(f, iter) {
  for (const a of iter) {
    if (!f(a)) return;
    yield a;
  }
}

function *map(f, iter) {
  for (const a of iter) yield f(a);
}

function *filter(f, iter) {
  for (const a of iter) if (f(a)) yield a;
}

function reduce(f, acc, iter) {
  if (arguments.length == 2) {
    iter = acc[Symbol.iterator]();
    acc = iter.next().value;
  }
  for (const a of iter) acc = f(acc, a);
  return acc;
}