Make next/router a client only API. (#443)

* Prevent using 'next/router' APIs inside 'getInitialProps'

* Remove incorrect documentation.

* Make next/router a client only API.

examples/using-router/components/Header.js

@@ -24,8 +24,6 @@ export default () => (
   <div>
     <Link href='/'>Home</Link>
     <Link href='/about'>About</Link>
-    <div>
-      <small>Now you are in the route: {Router.route} </small>
-    </div>
+    <Link href='/error'>Error</Link>
   </div>
 )

examples/using-router/pages/error.js

@@ -0,0 +1,16 @@
+import React from 'react'
+import Header from '../components/Header'
+import Router from 'next/router'
+
+const ErrorPage = ({ aa }) => (
+  <div>
+    <Header />
+    <p>This should not be rendered via SSR</p>
+  </div>
+)
+
+ErrorPage.getInitialProps = () => {
+  console.log(Router.pathname)
+}
+
+export default ErrorPage

lib/router/index.js

@@ -6,7 +6,7 @@ let router = null
 const SingletonRouter = {}
 
 // Create public properties and methods of the router in the SingletonRouter
-const propertyFields = ['route', 'components', 'pathname', 'query']
+const propertyFields = ['components', 'pathname', 'route', 'query']
 const methodFields = ['push', 'replace', 'reload', 'back']
 
 propertyFields.forEach((field) => {
@@ -16,6 +16,7 @@ propertyFields.forEach((field) => {
   // proper way to access it
   Object.defineProperty(SingletonRouter, field, {
     get () {
+      throwIfNoRouter()
       return router[field]
     }
   })
@@ -23,29 +24,33 @@ propertyFields.forEach((field) => {
 
 methodFields.forEach((field) => {
   SingletonRouter[field] = (...args) => {
+    throwIfNoRouter()
     return router[field](...args)
   }
 })
 
-// This is an internal method and it should not be called directly.
-//
-// ## Client Side Usage
-// We create the router in the client side only for a single time when we are
-// booting the app. It happens before rendering any components.
-// At the time of the component rendering, there'll be a router instance
-//
-// ## Server Side Usage
-// We create router for every SSR page render.
-// Since rendering happens in the same eventloop this works properly.
+function throwIfNoRouter () {
+  if (!router) {
+    const message = 'No router instance found.\n' +
+      'You should only use "next/router" inside the client side of your app.\n'
+    throw new Error(message)
+  }
+}
+
+// Export the SingletonRouter and this is the public API.
+export default SingletonRouter
+
+// INTERNAL APIS
+// -------------
+// (do not use following exports inside the app)
+
+// Create a router and assign it as the singleton instance.
+// This is used in client side when we are initilizing the app.
+// This should **not** use inside the server.
 export const createRouter = function (...args) {
   router = new _Router(...args)
   return router
 }
 
-// Export the actual Router class, which is also use internally
-// You'll ever need to access this directly
+// Export the actual Router class, which is usually used inside the server
 export const Router = _Router
-
-// Export the SingletonRouter and this is the public API.
-// This is an client side API and doesn't available on the server
-export default SingletonRouter

server/render.js

@@ -3,7 +3,7 @@ import { createElement } from 'react'
 import { renderToString, renderToStaticMarkup } from 'react-dom/server'
 import requireModule from './require'
 import read from './read'
-import { createRouter } from '../lib/router'
+import { Router } from '../lib/router'
 import Head, { defaultHead } from '../lib/head'
 import App from '../lib/app'
 
@@ -56,12 +56,12 @@ async function doRender (req, res, pathname, query, {
   if (res.finished) return
 
   const renderPage = () => {
-    const router = createRouter(pathname, query)
     const app = createElement(App, {
       Component,
       props,
-      router
+      router: new Router(pathname, query)
     })
+
     const html = (staticMarkup ? renderToStaticMarkup : renderToString)(app)
     const head = Head.rewind() || defaultHead()
     return { html, head }