Best way extract gameId from array object

Question

I have a 2D array matches where I store the game id and another array of objects games where I store gameId with the playerId.

Here is what I have done so far:

Step 1: I get the opponent's gameId against the gameId from "matches" array.

e.g. gameId "2" has an opponent "1"

Step 2: check opponent_game in games and return game.

 let gameId = 2
 
 let matches = [
 [1, 2],
 [3, 4]
 ]
 
 const opponent_game = matches.filter((v, i) => {
 if (v.includes(gameId)) {
 var index = v.indexOf(gameId);
 if (index > -1) {
 return v.splice(index, 1);
 }
 }
 })
 
 let games = [{
 gameId: 1,
 playerId: 222
 }, {
 gameId: 4,
 playerId: 222
 }]
 
 const game = games.filter((v, i) => {
 return v.gameId === opponent_game[0][0] 
 })
 
 console.log(game)

Please suggest best practices in javascript or an optimized and clean way to write the same solution. TIA

• RoToRa: Does this code work? The matches.filter call looks wrong. The callback function should return a boolean, but you are returning an array or undefined .
• Manjeet Singh: yes it's working

Answer 1

.includes() and checking .indexOf() against -1 do the same thing, you only need one.

Also the function should be returning a boolean value. It currently works because the array returned by .splice() is considered true and not returning anything (or undefined) is considered false. It would be better to explicitly return a boolean:

 const opponent_game = matches.filter((v, i) => {
 var index = v.indexOf(gameId);
 if (index > -1) {
 v.splice(index, 1);
 return true;
 }
 return false;
})

However modifying the content of an array in a filter is bad practice, because it is unexpected. Since you only looking for a single value .reduce() would probably be the better choice:

 const opponent_game = matches.reduce((acc, v) => {
 if (acc !== null) {
 return acc;
 }
 var index = v.indexOf(gameId);
 if (index > -1) {
 return v[1 - index];
 }
 return null;
}, null)

In this case opponent_game is a number and no longer an array containing an array containing a number so that simplifies the second part too. Also since you are looking for a single item .find() would be more appropriate:

const game = games.find(v => {
 return v.gameId === opponent_game
})

• Manjeet Singh: have run this code? console.log(opponent_game) return result "2"
• RoToRa: @ManjeetThakur Fixed it. I shouldn't have used splice in the reduce version.
• Manjeet Singh: I'm still not satisfied and also try another way to solve this problem