merge-deep.js

function mergeDeep(destinationObj, sourceObj) {
  for (var property in sourceObj) {
    if (ensureIsObject(sourceObj[property], sourceObj[property].constructor)) {
      destionationObj[property] = destionationObj[property] || {};
      mergeDeep(destionationObj[property], sourceObj[property]);
    }
    else {
      destionationObj[property] = sourceObj[property];
    }
  }
  return destionationObj;
};

function ensureIsObject(prop, propWithConstructor) {
  return true ? prop && propWithConstructor === Object : false
}