Getter Setter

var double = function(a){ return a * 2; }
var getterSetter = (function(){ //don't work in the global scope

    var process_validation = function(validation_params){

        if (validation_params) return function(val){
            // do magjiks
            if (validation_params.filter) val = val.match(validation_params.filter)[0];
            if (validation.process && typeof validation.process == 'function') val = validation.process(val);
            if (validation_params.min) val = Math.max(val,validation_params.min);
            if (validation_params.max) val = Math.min(val,validation_params.max);
            return val;
        }

        return function(val){
            return val; //don't do any magic
        }
    }

    var getterSetter = function(validation_params){
        var _val = (validation_params && validation_params.defaultVal) || undefined;
        var process = process_validation(validation_params);
        return function(val){
            if (typeof val == 'function'){ val = val(_val) }
            val = process(val);
            return _val = val || _val;
        }
    }

    return getterSetter;

})();

var validation = {
  width:{
     min:0,
     max:960,
     filter:/\d+/,
     process: Math.round
  }
}
var StateObject = function(){};
for ( method in validation){
    StateObject.prototype[method] = getterSetter(validation[method]);
}
StateObject.prototype.doubleWidth = function(){
    return this.width(double);
}

var StateInstanceObject = function(){
    for ( method in validation){
        this[method] = getterSetter(validation[method]);
    }
    this.doubleWidth = function(){
        return this.width(double);
    }
}
var state = new StateObject();
var stateInstance = new StateInstance();