Updates code comments.

Author: ctrlplusb

src/index.js

@@ -1,4 +1,5 @@
 /* @flow */
+// Extracted from: https://github.com/apollostack/react-apollo/blob/master/src/server.ts
 
 // eslint-disable-next-line import/no-extraneous-dependencies
 import { Children, Element } from 'react';
@@ -8,6 +9,8 @@ type Context = { [key: string]: any; };
 type ElementVisitor =
   (element: React$Element, instance: ?Function, context: Context) => boolean | void;
 
+export const isPromise = (x : any) => typeof x === 'object' && typeof x.then === 'function';
+
 // Recurse an React Element tree, running visitor on each element.
 // If visitor returns `false`, don't call the element's render function
 //   or recurse into its child elements
@@ -16,16 +19,14 @@ export default function reactTreeWalker(
   visitor: ElementVisitor,
   context: Context = {},
 ) {
-  const Component = element.type;
-
-  // a stateless functional component or a class
-  if (typeof Component === 'function') {
+  // Is this element a Component?
+  if (typeof element.type === 'function') {
+    const Component = element.type;
     const props = Object.assign({}, Component.defaultProps, element.props);
     let childContext = context;
     let child;
 
-    // Are we are a react class?
-    // http://bit.ly/2j9Ifk3
+    // Is this a class component? (http://bit.ly/2j9Ifk3)
     const isReactClassComponent = Component.prototype &&
       (Component.prototype.isReactComponent || Component.prototype.isPureReactComponent);
 
@@ -35,43 +36,57 @@ export default function reactTreeWalker(
       instance.props = instance.props || props;
       instance.context = instance.context || context;
 
-      // Override setState to just change the state, not queue up an update.
-      //   (we can't do the default React thing as we aren't mounted "properly"
-      //   however, we don't need to re-render as well only support setState in
-      //   componentWillMount, which happens *before* render).
+      // Make the setState synchronous.
       instance.setState = (newState) => {
         instance.state = Object.assign({}, instance.state, newState);
       };
 
+      // Call componentWillMount if it exists.
       if (instance.componentWillMount) {
         instance.componentWillMount();
       }
 
+      // Ensure the child context is initialised if it is available. We will
+      // need to pass it down the tree.
       if (instance.getChildContext) {
         childContext = Object.assign({}, context, instance.getChildContext());
       }
 
+      // Hit up our visitor!
       if (visitor(element, instance, context) === false) {
+        // Visitor returned false, indicating a desire to not traverse.
         return;
       }
 
+      // Get the render output as the child.
       child = instance.render();
-    } else { // just a stateless functional
+    } else {
+      // Stateless Functional Component
+
+      // Hit up our visitor!
       if (visitor(element, null, context) === false) {
+        // Visitor returned false, indicating a desire to not traverse.
         return;
       }
 
+      // Get the output for the function, as the child.
       child = Component(props, context);
     }
 
+    // Only continue walking if a child exists.
     if (child) {
       reactTreeWalker(child, visitor, childContext);
     }
-  } else { // a basic string or dom element, just get children
+  } else {
+    // This must be a basic element, such as a string or dom node.
+
+    // Hit up our visitor!
     if (visitor(element, null, context) === false) {
+      // Visitor returned false, indicating a desire to not traverse.
       return;
     }
 
+    // If the element has children then we will walk them.
     if (element.props && element.props.children) {
       Children.forEach(element.props.children, (child: any) => {
         if (child) {