Javascript call object methods from array?

Question

I am trying to loop through an array of gameobjects and call their update methods. Gameobjects can have different update implementations (eg: update of enemy is different from update of friend), so I created an prototype inheritance chain. But I can't get it to work: while looping through all objects I don't seem to be able to call their update methods: the compiler says they don't exist. So my question is: is it possible in Javascript to loop trough an array of objects that share the same base class and call a method on them that can be overwritten by different sub-classes?

This is what I have so far, don't know where I went wrong...:

//base gameobject class 
function GameObject(name) {
    this.name = name
};
GameObject.prototype.update = function(deltaTime) {
    throw new Error("can't call abstract method!")
};

//enemy inherits from gameobject
function Enemy() {
    GameObject.apply(this, arguments)
};
Enemy.prototype = new GameObject();
Enemy.prototype.constructor = Enemy;
Enemy.prototype.update = function(deltaTime) {
    alert("In update of Enemy " + this.name);
};


var gameobjects = new Array();

// add enemy to array
gameobjects[gameobjects.length] = new Enemy("weirdenemy");

// this doesn't work: says 'gameobject doesn't have update method'
for (gameobject in gameobjects) {
    gameobject.update(1); // doesn't work!!
}

Answer 1

Its not a problem with your Inheritance chain, but with this construct

for(gameobject in gameobjects){
    gameobject.update(1); // doesn't work!!
} 

When you iterate an Array with for..in , the variable will have the index values only. So, gameobject will have 0 , 1 .. like that, in every iteration. It is not recommended to use for..in to iterate an Array.

You might want to use, Array.prototype.forEach , like this

gameobjects.forEach(function(gameObject) {
    gameObject.update(1);
});

Answer 2

When you iterate through an array with for ... in , the values of the loop variable will be the keys to the array, not the values.

You really shouldn't iterate through arrays that way anyway:

for (var i = 0; i < gameobjects.length; ++i)
    gameobjects[i].update(1);

Answer 3

Try this, it works for me: =)

 gameobjects.forEach(function(gameobject){
        gameobject.update(1); // doesn't work!!
    });