parsing.js

var TILEDMapClass = Class.extend({
    currMapData: null,
    numXTiles: 100,
    numYTiles: 100,
    tileSize: {
        "x": 64,
        "y": 64
    },

    pixelSize: {
        "x": 64,
        "y": 64
    },

    fullyLoaded: false,

    load: function (map) {
        xhrGet(map, function (data) {
            gMap.parseMapJSON(data.responseText);
        });
    },

    parseMapJSON: function (mapJSON) {
        gMap.currMapData = JSON.parse(mapJSON);
        
        var map = this.currMapData;
        this.numXTiles = map.width;
        this.numYTiles = map.height;
        this.tileSize.x = map.tilewidth;
        this.tileSize.y = map.tileheight;
        this.pixelSize.x = this.tileSize.x * this.numXTiles;
        this.pixelSize.y = this.tileSize.y * this.numYTiles;
        this.fullyLoaded = true;
    }
});

var gMap = new TILEDMapClass();