title: How do you know the parameters Model.prototype.save() function takes on mongoose?
body: <p>So, I know that the save function’s callback will accept at least two parameters, error, and the saved document. But when I try to check that on the <a href="https://mongoosejs.com/docs/api.html#model_Model-save" rel="nofollow noreferrer">documentation</a>, the only information I se regarding the callback is</p>
  <blockquote>
  <p>[fn] «Function» optional callback</p>
  </blockquote>
  <p>The question is, why is Mongoose ignoring the information about the callback’s argument?</p>
  <p>I read <a href="https://stackoverflow.com/questions/33019804/how-does-mongooses-save-callback-work">somewhere else</a> that there is even third argument it can take, &quot; The number of rows affected&quot;. How am I supposed to know about that, or if it is even true if it is not listed on the official documentation?</p>
  <p>The purpose of these questions is to understand how to search documentation and to understand what to expect when you do that. Thanks!</p>