JavaScript DRY Up Code, Avoid Repeat Object Key Exist Checks?

Question

Hey there hope all is well,

Just wrapping up a small coding assignment where i'd like to avoid repeating myself in the implementation

let matchScores = [
  {
    '0': { 'Team A': 3, 'Team B': 3 },
    '1': { 'Team D': 1, 'Team F': 0 },
    '2': { 'Team E': 2, 'Team C': 0 }
  },
  {
    '3': { 'Team E': 1, 'Team F': 2 },
    '4': { 'Team B': 0, 'Team D': 0 },
    '5': { 'Team C': 4, 'Team A': 2 }
  }
]

This is the input to the function which is array of objects that have a "match" results between two teams. Each element in the array is a different "day" of games that need to be appended to a total point score. The goal is to create a function that for each "day ill iterate through the array and sum up the points awarded for the winners of the matches.

If a team wins they are awarded 3 points, if there is a tie both teams are only awarded one point.

Expected Output

Match 1
Team A, 3 pts
Team B, 3 pts
Team C, 1 pt

Match 2
Team A, 4 pts
Team B, 3 pts
Team C, 3 pts

function calculateResults(matchDays) {

  let matchScore = {};
  matchDays.forEach((day, i) => {


    for (const [key, value] of Object.entries(day)) {
      let match = Object.entries(value);
      let team1 = match[0];
      let team2 = match[1];

      // team 1 win
      if (team1[1] > team2[1]) {
        // if team's score exists
        if (matchScore[team1[0]]) {
          // add value
          matchScore[team1[0]] += 3;
        } else {
          // create value
          matchScore[team1[0]] = 3;
        }
      }

      // team 2 win
      if (team1[1] < team2[1]) {
        // if team's score exists
        if (matchScore[team2[0]]) {
          matchScore[team2[0]] += 3;
        } else {
          matchScore[team2[0]] = 3;
        }
      }
      // tie
      if (team1[1] === team2[1]) {
        if (matchScore[team1[0]]) {
          matchScore[team1[0]] += 1;
        } else {
          matchScore[team1[0]] = 1;
        }

        if (matchScore[team2[0]]) {
          matchScore[team2[0]] += 1;
        } else {
          matchScore[team2[0]] = 1;
        }
      }
    }

  });
}

Here's my current implementation. Is there any way I can avoid repeating the object key value checks if it exists? Im currently trying to iterate through and store the value in matchScore

Answer 1

You can use the new(ish) nullish coalescing operator to convert undefined to 0, then just always do the addition:

// team 1 win
if (team1[1] > team2[1]) {
    matchScore[team1[0]] = matchScore[team1[0]] ?? 0 + 3; // ***
}

// team 2 win
if (team1[1] < team2[1]) {
    matchScore[team2[0]] = matchScore[team2[0]] ?? 0 + 3; // ***
}

// ...and so on...

?? evaluates its left-hand operand and, if that value is not undefined, takes that value as its result; if the left-hand value is undefined, ?? evaluates its right-hand operand and takes that value as its result.

If you need to target an environment that doesn't have ?? (yet), in this particular case you can use || (logical OR) instead. || does the same thing ?? does, but the check isn't just for undefined, but for any falsy value. In this particular case, that's fine.

---

You probably want else if and else in there as well:

if (team1[1] > team2[1]) {
    // team 1 win
    matchScore[team1[0]] = matchScore[team1[0]] ?? 0 + 3;
} else if (team1[1] < team2[1]) {
    // team 2 win
    matchScore[team2[0]] = matchScore[team2[0]] ?? 0 + 3;
} else {
    // tie
    matchScore[team1[0]] = matchScore[team1[0]] ?? 0 + 1;
    matchScore[team2[0]] = matchScore[team2[0]] ?? 0 + 1;
}