Fix shallow routing examples using old React lifecycle and deprecated props.url (#4950)

* replace componentWillReceiveProps by componentDidUpdate

* replace props.url by withRouter HOC

* fix deprecated `props.url` in with-shallow-routing example

examples/with-shallow-routing/pages/index.js

@@ -1,11 +1,11 @@
 import React from 'react'
 import Link from 'next/link'
-import Router from 'next/router'
+import Router, { withRouter } from 'next/router'
 import { format } from 'url'
 
 let counter = 1
 
-export default class Index extends React.Component {
+class Index extends React.Component {
   static getInitialProps ({ res }) {
     if (res) {
       return { initialPropsCounter: 1 }
@@ -23,24 +23,35 @@ export default class Index extends React.Component {
   }
 
   incrementStateCounter () {
-    const { url } = this.props
-    const currentCounter = url.query.counter ? parseInt(url.query.counter) : 0
+    const { router } = this.props
+    const currentCounter = router.query.counter
+      ? parseInt(router.query.counter)
+      : 0
     const href = `/?counter=${currentCounter + 1}`
     Router.push(href, href, { shallow: true })
   }
 
   render () {
-    const { initialPropsCounter, url } = this.props
+    const { initialPropsCounter, router } = this.props
 
     return (
       <div>
         <h2>This is the Home Page</h2>
-        <Link href='/about'><a>About</a></Link>
+        <Link href='/about'>
+          <a>About</a>
+        </Link>
         <button onClick={() => this.reload()}>Reload</button>
-        <button onClick={() => this.incrementStateCounter()}>Change State Counter</button>
+        <button onClick={() => this.incrementStateCounter()}>
+          Change State Counter
+        </button>
         <p>"getInitialProps" ran for "{initialPropsCounter}" times.</p>
-        <p>Counter: "{url.query.counter || 0}".</p>
+        <p>
+          Counter: "{router.query.counter || 0}
+          ".
+        </p>
       </div>
     )
   }
 }
+
+export default withRouter(Index)

readme.md

@@ -600,14 +600,17 @@ const as = href
 Router.push(href, as, { shallow: true })
 ```
 
-Now, the URL is updated to `/?counter=10`. You can see the updated URL with `this.props.url` inside the `Component`.
+Now, the URL is updated to `/?counter=10`. You can see the updated URL with `this.props.router.query` inside the `Component` (make sure you are using [`withRouter`](#using-a-higher-order-component) around your `Component` to inject the `router` prop).
 
-You can watch for URL changes via [`componentWillReceiveProps`](https://facebook.github.io/react/docs/react-component.html#componentwillreceiveprops) hook as shown below:
+You can watch for URL changes via [`componentDidUpdate`](https://reactjs.org/docs/react-component.html#componentdidupdate) hook as shown below:
 
 ```js
-componentWillReceiveProps(nextProps) {
-  const { pathname, query } = nextProps.url
-  // fetch data based on the new query
+componentDidUpdate(prevProps) {
+  const { pathname, query } = this.props.router
+  // verify props have changed to avoid an infinite loop
+  if (query.id !== prevProps.router.query.id) {
+    // fetch data based on the new query
+  }
 }
 ```