Question

I have been trying all day to find a way to make this work. It’s really bugging me. I’ve read loads of articles on OOP and although i know my code is not perfect, I can’t seem to get around the initial problem that I have outlined in my code below.

All of the code works except the dynamic getter/setter – If you read my comments in the code or run the code you can easily see why.

I have a feeling what I’m trying to do can’t be done. Can someone tell me where I’m going wrong, or if It can’t be done the way i have proposed.

            var ext = {
        db: {
            string: function(def){
                def=def || {};
                def.type = "string";
                return def;
            },
            autoId: function(def){
                def=def || {};
                def.defaultvalue = function(){
                    return Math.uuid(def.length, def.radix)
                    return def;
                }
            }
        },
    }
    /*
     * @ext.base:       base class I can build out with common methods
     *                  
     */
    ext.base = function(){
        /*
         * place holder for the raw object data - 
         * 
         * {a:"martin webb",b:"is struggling with this"
         * 
         */
        this._rawdata={}; // this can later be strigified for storage; 

    };
    ext.base.prototype ={
        init:function(o){
            // pass in rawdata;
            this.load(o);
        },
        put:function(){
            //code removed
        },
        load: function(rawdata){
            this._rawdata=rawdata || {};
        }

    }
    /*
     * @ext.kind:       builds a new object we can use to make entities from our kind
     *                  martin=new people();
     * 
     */
    ext.db.kind=function(o){
        this._kind=function(o){this.init(o);} //this will pass any passed in object in the base class at init;
        this._kind.prototype = ext.base.prototype;

        var self=this;

        var prop,i=97; //ascii for "a";
        for (prop in o){
            if (o.hasOwnProperty(prop)) {
                /*
                 * This is like a dynamic getter setter, we are adding it to the prototype;
                 * 
                 * if you run the code when the function below is called
                 * value="martin webb" I need the var i to equal 97, and prop to = "name"
                 * in the function. I need a way to pass in and conserver these dynamic values
                 */
                this._kind.prototype[prop] = 
                    function(value){
                        if (value) {
                            self.rawdata[i] = value; //ERROR i=99!
                        }
                        return self.rawdata[i] ; //get the correct data using the key 
                    };

                    i++;
                }

        }
        return this._kind; // return our new object so we can use it like var martin=new people();
    }
    debugger;
    //lets make a new kind;
    var people={};
    people.name=ext.db.string();
    people.info=ext.db.string();
    people = new ext.db.kind(people);
    //and now make some entities usinhg it;
    var martin=new people();


    //THE CODE WILL GO WRONG HERE, THE SETTER WILL NOT WORK (SEE ABOVE)

    martin.name("martin webb")
    martin.info("is struggling with this code")

    var mike = new people({
        a: "mike",
        b: "has the solution"
    });
    console.log(mike.name()) //--> mike

Answer 1

I have found the solution. The answer was to use an enclosure and trap the loop index (i).

This was beautifully explained in the article by

Explaining javascript Scope and closures

The alteration to my code is as follows and works a treat!

           var prop, i = 97; //ascii for "a";
            //loop each property and make our own get/setter that works
            //off our underlying compressed rawdata;
            for (prop in o) {
                if (o.hasOwnProperty(prop)) {
                    /*
                     * this is the trick
                     * use an enclosure and pass our loop index in the bottom
                     * with a self calling function, this locks the value of i;
                     */
                    this._kind.prototype[prop] = function(k){
                        return function(value){
                            var key=String.fromCharCode(k);
                            //if we have a value passed in set it!
                            if (value){
                                this._rawdata[key]=value;
                            }
                            //always return our value;
                            return this._rawdata[key];
                        };
                      }(i); //here we call our function and lock index i;

                    i++;
                }//end loop;