docs: fix some more examples that still use callbacks re: #13616

docs/async-await.md

@@ -11,27 +11,7 @@ This is especially helpful for avoiding callback hell when executing multiple as
 Each of the three functions below retrieves a record from the database, updates it, and prints the updated record to the console.
 
 ```javascript
-// Works.
-function callbackUpdate() {
-  MyModel.findOne({ firstName: 'franklin', lastName: 'roosevelt' }, function(err, doc) {
-    if (err) {
-      handleError(err);
-    }
-
-    doc.middleName = 'delano';
-
-    doc.save(function(err, updatedDoc) {
-      if (err) {
-        handleError(err);
-      }
-
-      // Final logic is 2 callbacks deep
-      console.log(updatedDoc);
-    });
-  });
-}
-
-// Better.
+// Using promise chaining
 function thenUpdate() {
   MyModel.findOne({ firstName: 'franklin', lastName: 'roosevelt' })
     .then(function(doc) {
@@ -44,7 +24,7 @@ function thenUpdate() {
     });
 }
 
-// Best?
+// Using async/await
 async function awaitUpdate() {
   try {
     const doc = await MyModel.findOne({

docs/queries.md

@@ -104,44 +104,16 @@ A full list of [Query helper functions can be found in the API docs](api/query.h
   </a>
 </h2>
 
-Mongoose queries are **not** promises. They have a `.then()`
-function for [co](https://www.npmjs.com/package/co) and
-[async/await](http://thecodebarbarian.com/common-async-await-design-patterns-in-node.js.html)
-as a convenience. However, unlike promises, calling a query's `.then()`
-can execute the query multiple times.
-
-For example, the below code will execute 3 `updateMany()` calls, one
-because of the callback, and two because `.then()` is called twice.
+Mongoose queries are **not** promises.
+Queries are [thenables](https://masteringjs.io/tutorials/fundamentals/thenable), meaning they have a `.then()` method for [async/await](http://thecodebarbarian.com/common-async-await-design-patterns-in-node.js.html) as a convenience.
+However, unlike promises, calling a query's `.then()` executes the query, so calling `then()` multiple times will throw an error.
 
 ```javascript
-const q = MyModel.updateMany({}, { isDeleted: true }, function() {
-  console.log('Update 1');
-});
-
-q.then(() => console.log('Update 2'));
-q.then(() => console.log('Update 3'));
-```
+const q = MyModel.updateMany({}, { isDeleted: true });
 
-Don't mix using callbacks and promises with queries, or you may end up
-with duplicate operations. That's because passing a callback to a query function
-immediately executes the query, and calling [`then()`](https://masteringjs.io/tutorials/fundamentals/then)
-executes the query again.
-
-Mixing promises and callbacks can lead to duplicate entries in arrays.
-For example, the below code inserts 2 entries into the `tags` array, **not** just 1.
-
-```javascript
-const BlogPost = mongoose.model('BlogPost', new Schema({
-  title: String,
-  tags: [String]
-}));
-
-// Because there's both `await` **and** a callback, this `updateOne()` executes twice
-// and thus pushes the same string into `tags` twice.
-const update = { $push: { tags: ['javascript'] } };
-await BlogPost.updateOne({ title: 'Introduction to Promises' }, update, (err, res) => {
-  console.log(res);
-});
+await q.then(() => console.log('Update 2'));
+// Throws "Query was already executed: Test.updateMany({}, { isDeleted: true })"
+await q.then(() => console.log('Update 3'));
 ```
 
 <h2 id="refs"><a href="#refs">References to other documents</a></h2>