Function extend

static/vuejs/vue.js:154–159

* Mix properties into target object.

(to, _from)

 * Mix properties into target object.
 */
function extend (to, _from) {
  for (var key in _from) {
    to[key] = _from[key];
  }
  return to
}

/**
 * Quick object check - this is primarily used to tell