title: Can two GraphQLSchema instances be merged?
body: <p>I'm looking to write a function like <code>Object.assign</code> or <code>_.merge</code>, but that operates on <code>GraphQLSchema</code> objects.</p>
  
  <p>Suppose I have two instances of <a href="http://graphql.org/graphql-js/type/#graphqlschema" rel="nofollow noreferrer"><code>GraphQLSchema</code></a>, call them Base and Other, and I would like to merge Other into Base to produce a new instance Result such that</p>
  
  <ul>
  <li>Fields present in exactly one of Base or Other are defined in Result by their original <code>GraphQLFieldConfig</code></li>
  <li>Fields present in both are reduced to the <code>GraphQLFieldConfig</code> in Other.</li>
  </ul>
  
  <p>It looks as though there is no documented means to do this. Is that correct? If I went the (considerably more dangerous) undocumented route, I've noticed that I could exploit internal properties of the object:</p>
  
  <p><a href="https://i.stack.imgur.com/55oqp.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/55oqp.png" alt="enter image description here"></a>, but I'd prefer not to do that.</p>
  
  <p>Any advice would be appreciated. Thanks in advance!</p>