Reference a function property of object by passed variable

Question

I'm very new to JavaScript, and programming in general. This question is in the context of an RPG. I have a character object in a combat function, trying to call an ability function based on a) predefined character class, and b) input:

// player example
var player = {
  this.pClass = 0; // denotes character class; could also be 1 or 2
}  

// ability list
var ability = {
  // first character class
  0: {
    1: function() {some action;},
    2: function() {some other action;}
  },
  // second character class
  1: {
  // same deal here
  }
};

var input = prompt("Enter an action number:");

I would like to be able to call the action by passing the player class and selected number, something like:

ability.{player.pClass}.{input}();

Am I approaching this in the right way, at all? I'd prefer not to iterate if...else if statements for every option, if possible. Thanks for the assistance.

I recommend you start learning JavaScript here jqfundamentals.com/chapter/javascript-basics. You seem to have some misunderstanding of basic syntax and concepts... — elclanrs
– elclanrs, Commented Apr 27, 2013 at 2:24
@elclanrs: No doubt of that. This project is mostly to teach myself JavaScript. Thanks for the reference. — TxRob
– TxRob, Commented Apr 27, 2013 at 2:26

Bart · Accepted Answer · 2013-04-27 02:36:11Z

1

You can access an object's properties by using square brackets:

var abilities = {
    fireball: function() { ... }
};

abilities["fireball"];
abilities.fireball; // equivalent, but only if the index is a valid js identifier

While you can use numeric indices, I would suggest a more object-oriented way:

// define what a player is and can do
var Player = function(pClass) {
    this.pClass= pClass;
};

Player.prototype.useAbility = function(name) {
    if (this.pClass.abilities[name]) { // make sure this player can use the ability
        this.pClass.abilities[name]();
    }
};

// define what a class is
var PClass = function(name) {
    this.name = name;
    this.abilities = {};
};

// define "mage" class
PClass.mage = new PClass("mage");
PClass.mage.abilities["fireball"] = function() { ... }
PClass.mage.abilities["hex"] = function() { ... }

PClass.warrior = new PClass("warrior");
PClass.warrior.abilities["riposte"] = function() { ... }

// create a new player
var bartTheFearsome = new Player(PClass.mage);
bartTheFearsome.useAbility("fireball");
bartTheFearsome.useAbility(prompt("enter ability name")); // enter "fireball" or "hex"

If you're new to (object oriented) programming, here's a good place to start.

answered Apr 27, 2013 at 2:36

Bart

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2 Comments

TxRob Over a year ago

Thanks for the reference link. The Mozilla site has been of great help so far. I like your approach for a more text-oriented game, but my method will ultimately be to click a button to select an action, in which case the name of the reference doesn't matter as much. I may use this alternative elsewhere, however. Thanks again.

Bart Over a year ago

Names matter primarily for the programmer. 1 week from now, you're not going to remember that "0" means "mage" and "1" means "warrior". PClass.mage.abilities["fireball"] is descriptive. ability[0][1] isn't.

David G · Accepted Answer · 2013-04-27 02:25:37Z

1

Use the square bracket notation to allow dynamic access of property names:

ability[player.pClass][input]();

But your object literal shouldn't have numeric property names. Try giving them real meaningful names instead. Otherwise, if this is what you intended, use an array instead:

var abilities = [function() {..}, function() {..}];

edited Apr 27, 2013 at 2:25

answered Apr 27, 2013 at 2:18

David G

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2 Comments

TxRob Over a year ago

Thanks. I wasn't sure which approach to take, so that help clarify. However, would your initial response work as well? What's the advantage of referencing by name, rather than a numeric list?

David G Over a year ago

@RobRosson It just makes more sense. Your code can work fine with numeric names, but if you're using them on an object literal it's probably a sign that you could be doing so without.

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