flawless.js

function chanceToWin() {
  return Math.random() < 0.5;
}

function howManyMatchesToGoFlawless() {
  let matches = 0;
  let wins = 0;
  while (wins < 7) {
    if (chanceToWin()) {
      wins++;
    } else {
      wins = 0;
    }
    matches++;
  }
  return matches;
}

function howManyMatchesToGoFlawlessOnAverage() {
  const n = 2e6;
  return iterAverage(iterMap(iterRange(n), howManyMatchesToGoFlawless));
}

function* iterRange(n) {
  for (let i = 0; i < n; i++) {
    yield i;
  }
}

function* iterMap(items, fn) {
  for (const x of items) {
    yield fn(x);
  }
}

function iterAverage(items) {
  let sum = 0;
  let n = 0;
  for (const x of items) {
    sum += x;
    n++;
  }
  return sum / n;
}

console.log(howManyMatchesToGoFlawlessOnAverage());