Merge pull request #8 from SathishGovindaraju/master

Added preRender callback

README.md

@@ -67,6 +67,15 @@ For example:
     // Other callbacks
   }));  
 ```
+### `preRender`
+
+Callback function called before rendering `App`.
+This callback can either be a normal function which returns a valid component or it can return a `Promise` which then resolves and returns a valid component.
+The function accepts the following parameters:
+
+* `component` - The `StaticRouter` wrapped around the `App`.
+
+> This callback could be used to wrap the `component` with any other higher-order component before it gets rendered
 
 ### `onError`
 

index.js

@@ -6,14 +6,15 @@ const server = ({
   App,
   onError,
   onRedirect,
-  onRender
+  onRender,
+  preRender = router => router
 }) =>
   async (ctx, next) => {
     try {
       const location = ctx.request.url;
       const routerContext = {};
 
-      const view = renderToString(
+      const router = (
         <StaticRouter
           location={location}
           context={routerContext}
@@ -22,6 +23,12 @@ const server = ({
         </StaticRouter>
       );
 
+      const updatedComponent = await preRender(router);
+
+      if (!updatedComponent) throw new Error('No component returned from preRender');
+
+      const view = renderToString(updatedComponent);
+
       ctx.state = {
         ...ctx.state,
         routerContext

index.spec.js

@@ -1,6 +1,6 @@
 import sinon from 'sinon';
 import React from 'react';
-import { Route, Redirect } from 'react-router';
+import { Route, Redirect, StaticRouter } from 'react-router';
 import koaReactRouter from './index';
 
 const Container = ({ children }) =>
@@ -287,3 +287,47 @@ test('sets doctype in response body', async () => {
   expect(next.calledOnce).toBe(true);
 });
 
+test('calls preRender with StaticRouter as argument', async () => {
+  const preRender = sinon.sandbox.spy();
+  const callbacks = mockCallbacks();
+  callbacks.preRender = preRender;
+
+  const ctx = {
+    request: { url: '/away' },
+    response: {}
+  };
+  const next = sinon.spy();
+
+  await koaReactRouter({
+    App,
+    ...callbacks
+  })(ctx, next);
+
+  const expected = (
+    <StaticRouter location={ctx.request.url} context={{}}>
+      <App />
+    </StaticRouter>
+  );
+  expect(preRender.calledOnce).toBe(true);
+  expect(JSON.stringify(preRender.args[0][0])).toBe(JSON.stringify(expected));
+});
+
+test('should throw an error if preRender callback doesn\'t return component', async () => {
+  const preRender = () => {};
+  const callbacks = mockCallbacks();
+  callbacks.preRender = preRender;
+
+  const ctx = {
+    request: { url: '/away' },
+    response: {}
+  };
+  const next = sinon.spy();
+
+  await koaReactRouter({
+    App,
+    ...callbacks
+  })(ctx, next);
+
+  expect(callbacks.onError.calledOnce).toBe(true);
+  expect(callbacks.onError.args[0][1].message).toEqual('No component returned from preRender');
+});