Given a very long array of black and white balls. Assuming you can only swap any two balls at a time, please bring all the white balls to front and black balls to end.

getArrangedBlackWhiteBalls.js

const isWhiteBall = ball => ball === 'W';

const arrangeBlackWhiteBalls = (whiteBalls, blackBalls) => ball => {
  if (isWhiteBall(ball)) whiteBalls.push(ball);
  else blackBalls.push(ball);
}

const getArrangedBlackWhiteBalls = ballsArr => {
  const ballsRearranged = [];
  const whiteBalls = [];
  const blackBalls = [];
  ballsArr.map(arrangeBlackWhiteBalls(whiteBalls, blackBalls));
  return whiteBalls.concat(blackBalls);
}

console.log(getArrangedBlackWhiteBalls(['W', 'B', 'W', 'B', 'B', 'B', 'W', 'B']));