manifest.js

function Manifest(defaultObj) {
  this.data = defaultObj || {};
}
Manifest.prototype.render = function() {
  console.log(JSON.stringify(this.data));
};
Manifest.prototype.set = function(k, v) {
  this.data[k] = v;
  this.render();
};
Manifest.prototype.get = function(k) {
  return this.data[k];
};

var manifest = new Manifest();
manifest.set('name', 'My App');