Deep extend for simple JSON objects

deep-extend.js

function deepExtend(target, source) {
  Object.keys(source).forEach(function(key) {
    var value = source[key];
    var dest = target[key];
    var sourceType = typeof value;
    var destType = typeof target[key];

    if (Array.isArray(value) && Array.isArray(dest))
      target[key] = dest.concat(value);
    else if (sourceType === destType && sourceType === 'object')
      deepExtend(dest, value);
    else
      target[key] = value;
  });
  return target;
}