This JavaScript class wraps an Object to provide useful hash table / dictionary functionality. All data is maintained in the underlying Object. It doesn't pollute Object.prototype, so it plays nice with jQuery. See dict-example.js for examples.

dict-example.js

map = {
  "USA": { "Detroit": 23, "Cambridge": 5, "Cupertino": 0.5 },
  "Canada": { "Waterloo": 1 },
  "Switzerland": { "Geneva": 0.5 }
}
d = new Dict(map);

d.getDict("USA").get("Detroit"); // => 23

d.getDict("China", {}).get("Beijing", 0); // => 0

d.getDict("USA").keys() // => ["Detroit", "Cambridge", "Cupertino"]

d.getDict("USA").set("Cambridge", 6);
d.getDict("USA").get("Cambridge"); // => 6
map.USA.Cambridge; // => 6

dict.js

Dict = function (obj) { this.obj = obj ? obj : {}; };
Dict.prototype = {
    get: function (key, d) {
        return typeof(this.obj[key]) === 'undefined' ? d : this.obj[key];
    },
    getDict: function (key, d) {
        result = typeof(this.obj[key]) === 'undefined' ? d : this.obj[key];
        return new Dict(result);
    },
    set: function (key, value) { this.obj[key] = value; },
    map: function (f) {
        if (typeof(f) !== 'function') { return []; }
        result = [];
        for (key in this.obj) {
            if (this.obj.hasOwnProperty(key)) {
                result.push(f(key, this.obj[key]));
            }
        }
        return result;
    },
    keys: function () { return this.map(function (k, v) { return k; }); },
    values: function () { return this.map(function (k, v) { return v; }); }
}