Get objects position in array

Question

I have an array players[]

function that gets certain object from such array by looking up its gameSocketId value and returns that object

getUserInfo : function(user)
        {
            var userInfo = Game.players.filter(function(e) {
                return e.gameSocketId === user;
            }).pop();

            return userInfo;
        }

so I store it in a variable like var user = getUserInfo(userId) How can I than find out what is the position of user in array of players[] knowing all info about it?

Benjamin Gruenbaum · Accepted Answer · 2015-04-10 21:04:19Z

Use .findIndex:

getUserInfo : function(user)
    {
        var userInfoIndex = Game.players.findIndex(function(e) {
            return e.gameSocketId === user;
        });

        return userInfoIndex;
    }

Note that .findIndex, while fully specified is not included in most JS engines by default yet - there is a polyfill on mdn:

if (!Array.prototype.findIndex) {
  Array.prototype.findIndex = function(predicate) {
    if (this == null) {
      throw new TypeError('Array.prototype.findIndex called on null or undefined');
    }
    if (typeof predicate !== 'function') {
      throw new TypeError('predicate must be a function');
    }
    var list = Object(this);
    var length = list.length >>> 0;
    var thisArg = arguments[1];
    var value;

    for (var i = 0; i < length; i++) {
      value = list[i];
      if (predicate.call(thisArg, value, i, list)) {
        return i;
      }
    }
    return -1;
  };
}

This polyfill works on ES3 and ES5 browsers just fine :)

Of course, one can also use a normal for loop to do this which works all the way through ES1 - but then you don't get the fun syntax that conveys intent pretty clearly:

getUserInfo : function(user) {
    for(var i = 0; i < Game.players.length; i++){
        if(Game.players[i].gameSocketId === user) return i;
    }
    return -1;
}

We don't always have to be clever :) Of course, we can also always be inefficient and just call .indexOf after obtaining the item using your original method.

KJ Price · Accepted Answer · 2015-04-10 21:02:17Z

1

The second param of Array.filter is the index for the current item. The below will still return you the userInfo that you originally specified plus you can use the index for whatever you want.

    getUserInfo : function(user)
    {
       var playerIndex;
        var userInfo = Game.players.filter(function(e, index) {
            if (e.gameSocketId === user) {
                playerIndex = index;
                return true;
            }
        }).pop();

        console.log(Game.players[playerIndex]) // <- the player that is also "user"

        return userInfo;
    }

answered Apr 10, 2015 at 21:02

KJ Price

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Comments

SGD · Accepted Answer · 2015-04-10 21:05:15Z

0

How about using indexof()

getUserInfo : function(user){
    var userInfo = Game.players.filter(function(e) {
        return e.gameSocketId === user;
    }).pop();

    return userInfo;
}

// and later
var user = getUserInfo(userId)
console.log(Game.players.indexOf(user));

answered Apr 10, 2015 at 21:05

SGD

1,72615 silver badges18 bronze badges

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