Clue for Premier League Challenge...

premloop.js

let prem = {};

const tallyMatch = ({ team1, team2, score1, score2 }) => {
  // Check to see if the `prem` object
  // contains the team yet, and if not add it.
  if (!prem[team1.name]) {
    prem[team1.name] = { points: 0, name: team1.name };
  }
  if (!prem[team2.name]) {
    prem[team2.name] = { points: 0, name: team2.name };
  }

  // if a tie
  if (score1 === score2) {
    prem = {
      ...prem,
      [team1.name]: {
        ...prem[team1.name],
        points: prem[team1.name].points + 1
      },
      [team2.name]: {
        ...prem[team2.name],
        points: prem[team2.name].points + 1
      }
    };
    return;
  }

  // a win for team1
  if (score1 > score2) {
    prem = {
      ...prem,
      [team1.name]: {
        ...prem[team1.name],
        points: prem[team1.name].points + 3
      }
    };
  } else {
    // a win for team2
    prem = {
      ...prem,
      [team2.name]: {
        ...prem[team2.name],
        points: prem[team2.name].points + 3
      }
    };
  }
};

data.rounds.forEach(round => round.matches.forEach(tallyMatch));