Update example to remove AsyncGenerator (#654)

website/README.md

@@ -0,0 +1,3 @@
+# README
+
+Building the website requires that the documentation be generated from the root project into the `src/pages/docs` directory _first_. This can be done by `yarn gendocs` from the root of the repo.

website/src/pages/get-started.mdx

@@ -42,15 +42,61 @@ export const schema = new GraphQLSchema({
     fields: {
       greetings: {
         type: GraphQLString,
-        subscribe: async function* () {
-          for (const hi of ['Hi', 'Bonjour', 'Hola', 'Ciao', 'Zdravo']) {
-            yield { greetings: hi };
-          }
+        subscribe: async function () {
+          return new EventProvider().iterator();
         },
       },
     },
   }),
 });
+
+/**
+ * A toy event provider implementation. Will return a series of greetings with a small 
+ * delay in between each one.
+ */
+class EventProvider {
+  private readonly events = ['Hi', 'Bonjour', 'Hola', 'Ciao', 'Zdravo'];
+  private promiseReject: ((v?: any) => void) | null = null;
+  private closed = false;
+
+  close() {
+    if (this.closed) { return; }
+    if (this.promiseReject) { this.promiseReject('closed'); }
+    this.closed = true;
+  }
+
+  isClosed() { return this.closed || this.events.length === 0; }
+
+  async event() {
+    return await new Promise(async (resolve, reject) => {
+      this.promiseReject = reject;
+      setTimeout(() => resolve(this.events.shift()), 100);
+    });
+  }
+
+  iterator() {
+    const self = this;
+    return {
+      [Symbol.asyncIterator]() { return this; },
+      async next(): {
+        try {
+          if (!self.isClosed()) {
+            return { value: await self.event(), done: false };
+          }
+        } catch (e) {
+          return { value: undefined, done: true };
+        }
+      },
+      async return(v?: any) {
+        self.close();
+        return { value: v, done: true };
+      },
+      async throw(v?: any) {
+        return { value: undefined, done: true };
+      }
+    };
+  }
+}
 ```
 
 ### Start the server