Support arrays in server-side rendering (apollographql#1265)

React 16 now allows arrays to be returned from render. Update walkTree
to support this.

Author: clayne11

Changelog.md

@@ -5,7 +5,7 @@
 - Fix: ensure `client` option can be used with mutation query [#1145](https://github.com/apollographql/react-apollo/pull/1145)
 
 - Made `OptionProps.data`'s `TResult` partial [#1231](https://github.com/apollographql/react-apollo/pull/1231)
-
+- Support arrays being returned from render in SSR [#1158](https://github.com/apollographql/react-apollo/pull/1158)
 
 ### 1.4.16
 - upgrade to react-16

src/server.ts

@@ -37,6 +37,12 @@ export function walkTree(
     context: Context,
   ) => boolean | void,
 ) {
+  // elements can now be arrays (react@16)
+  if (Array.isArray(element)) {
+    element.forEach(item => walkTree(item, context, visitor));
+    return;
+  }
+
   const Component = element.type;
   // a stateless functional component or a class
   if (typeof Component === 'function') {
@@ -90,7 +96,11 @@ export function walkTree(
     }
 
     if (child) {
-      walkTree(child, childContext, visitor);
+      if (Array.isArray(child)) {
+        child.forEach(item => walkTree(item, context, visitor));
+      } else {
+        walkTree(child, childContext, visitor);
+      }
     }
   } else {
     // a basic string or dom element, just get children