Lazy stats accessor. Only recomputes value when necessary, but requires managing flags to avoid stale cache.

example-lazy-stats-accessor.js

// need a static local variable here to ensure all new stats have unique'ish ids.
// stacking the same modifier is not possible.  create a new object of the same modifier in order
// to apply the same effect twice.
var StatModifier = (function () {
  var idCounter = 0;
  
  return Base.extends({
    id: 0,
    name: '',
    affects: '',
    offset: 0,
    
    constructor: function (settings) {
      settings = settings || {};
      // override defaults with settings
      this.id = idCounter++;
      _.extend(this, settings);
    },
    
    toString: function () {
      return '[' + name + ', ' + affects + ', ' + offset + ']';
    },
  },
})();

var Stat = Base.extends({
  name: '',
  value: 0,
  baseValue: 0,
  modifiers: null,
  
  constructor: function (name, startingValue) {
    this.name = name || '';
    this.baseValue = startingValue || 0;
    this.value = this.baseValue;
    modifiers = {};
  },
  
  addModifier: function (mod) {
    // ignore this modifier if it's invalid or has no effect
    if (!mod || !mod.value) return;
    // warning: this modifier affects some other stat
    if (this.name == mod.affects) {
      console.log('Attempted to add stat modifier ' + mod.toString() + ' to wrong stat, ' + this.name);
      return;
    }
    // ignore this modifier if it's already applied.  NOTE: this occurance is a bug.  accounting elsewhere has failed D:
    if (this.modifiers[mod.id] === mod) {
      console.log('Attempting to re-add stat modifier, ' + mod.name + ', to stat, ' + this.name)
      return;
    }
    this.modifiers[mod.id] = mod;
    this.addOffset(mod.value);
  },
  
  // why addOffset?  because maybe some stats should extend and override this function.  why?
  // maybe some stats may have a floor/ceiling (clipped stat).  maybe some can be negative or must be positive, etc.
  // maybe some stats cannot change by more than 5 points (clipped offset), etc.
  // this should be a private function.  never use outside this class.
  addOffset = function (offset) {
    this.value += offset;
    if (this.value < 0) this.value = 0;
  },
  
  removeModifier = function (mod) {
    if (mod && this.modifiers[mod.id]) {
      this.modifiers[mod.id] = null;
    }
  },
});


// example: creating a stat
Game.player = new Player({
  skills: {
     botany: new Stat({
       name: 'botany'
     }),
  },
});

// example: creating stat modifier
brownThumb = new StatModifier({
  name: 'brown thumb',
  affects: 'botany',
  offset: -5,
});


// example: applying stat modifier
Game.player.skills.botany.addModifier(brownThumb);

// example: reading the base stat
value = Game.player.skills.botany.baseValue;

// example: reading the modified stat
value = Game.player.skills.botany.value;