code: function isWritable(obj, key) {
    var descriptor = Object.getOwnPropertyDescriptor(obj, key);
    return isUndefined(obj[key]) || descriptor && descriptor.writable
  }
docs: Check whether object's property could be overridden
  @param   { Object }  obj - source object
  @param   { String }  key - object property
  @returns { Boolean } -