Javascript: sort objects

Question

function Player() {
  var score;

  this.getScore = function() { return score; }
  this.setScore = function(sc) { score = sc; }
}

function compare(playerA, playerB) {
  return playerA.getScore() - playerB.getScore();
}

var players = [];

players['player1'] = new Player();
players['player2'] = new Player();

Array(players).sort(compare);

I have code that is similar to the above. When I step through the code with a debugger, the compare function never gets called and the array isn't sorted. I'm not sure what's wrong with my code?

Answer 1

It's not sorting because you have specified the keys that the variables within the array belong on. Sorting will only move the objects on integer-valued keys. You should see your sorting work if you create your array as follow:

var players = [new Player(), new Player()];

though, of course, it won't be very effective since you have neither a score on which to sort or a method of identifying them. This'll do it:

function Player(name, score) {
  this.getName = function() { return name; }
  this.getScore = function() { return score; }
  this.setScore = function(sc) { score = sc; }
}

function comparePlayers(playerA, playerB) {
  return playerA.getScore() - playerB.getScore();
}

var playerA = new Player('Paul', 10);
var playerB = new Player('Lucas', 5);
var playerC = new Player('William', 7);

var players = [playerA, playerB, playerC];

for (var i = 0; i < players.length; i++)
    alert(players[i].getName() + ' - ' + players[i].getScore());

players.sort(comparePlayers);

for (var i = 0; i < players.length; i++)
    alert(players[i].getName() + ' - ' + players[i].getScore());

Hope that helps.

Answer 2

The main problem lies in this line:

Array(players).sort(compare);

Array(something) makes an array with something as its element.

console.log(Array(players)); //[[player1, player2]]

Use numeric indexed array instead of using object like array as in players['player1']

Run the following code (replace console.log with alert if you don't have Firebug).

function Player() {
  var score;
  //return this.score - else it returns undefined
  this.getScore = function() { return this.score; } 
  this.setScore = function(sc) { this.score = sc; }
}

function compare(playerA, playerB) {
  console.log("called " + playerA.getScore() + " " + playerB.score);
  //compare method should return 0 if equal, 1 if a > b and -1 if a < b
  return (playerA.getScore() == playerB.getScore()) ? 0 
     : ((playerA.getScore() > playerB.getScore()) ? 1 : -1);
}

var players = [];

players[0] = new Player();
players[1] = new Player();
players[2] = new Player();
players[3] = new Player();
players[0].setScore(9);
players[1].score = 14;
players[2].score = 11;
players[3].score = 10;
players.sort(compare);
console.log(players);//prints sorted array