docs: add function example to props

Close #2493

docs/guide/essentials/passing-props.md

@@ -2,27 +2,24 @@
 
 <div class="vueschool"><a href="https://vueschool.io/lessons/how-to-pass-vue-router-params-as-props-to-components?friend=vuejs" target="_blank" rel="sponsored noopener" title="Learn how to pass props to route components with Vue School">Learn how to pass props to route components with a free lesson on Vue School</a></div>
 
-
 Using `$route` in your component creates a tight coupling with the route which limits the flexibility of the component as it can only be used on certain URLs.
 
 To decouple this component from the router use option `props`:
 
 **Instead of coupling to `$route`:**
 
-``` js
+```js
 const User = {
   template: '<div>User {{ $route.params.id }}</div>'
 }
 const router = new VueRouter({
-  routes: [
-    { path: '/user/:id', component: User }
-  ]
+  routes: [{ path: '/user/:id', component: User }]
 })
 ```
 
 **Decouple it by using `props`**
 
-``` js
+```js
 const User = {
   props: ['id'],
   template: '<div>User {{ id }}</div>'
@@ -34,8 +31,15 @@ const router = new VueRouter({
     // for routes with named views, you have to define the `props` option for each named view:
     {
       path: '/user/:id',
-      components: { default: User, sidebar: Sidebar },
-      props: { default: true, sidebar: false }
+      components: {
+        default: User,
+        sidebar: Sidebar
+      },
+      props: {
+        default: true,
+        // function mode, more about it below
+        sidebar: route => ({ search: route.query.q })
+      }
     }
   ]
 })
@@ -51,10 +55,14 @@ When `props` is set to `true`, the `route.params` will be set as the component p
 
 When `props` is an object, this will be set as the component props as-is. Useful for when the props are static.
 
-``` js
+```js
 const router = new VueRouter({
   routes: [
-    { path: '/promotion/from-newsletter', component: Promotion, props: { newsletterPopup: false } }
+    {
+      path: '/promotion/from-newsletter',
+      component: Promotion,
+      props: { newsletterPopup: false }
+    }
   ]
 })
 ```
@@ -63,10 +71,14 @@ const router = new VueRouter({
 
 You can create a function that returns props. This allows you to cast parameters into other types, combine static values with route-based values, etc.
 
-``` js
+```js
 const router = new VueRouter({
   routes: [
-    { path: '/search', component: SearchUser, props: (route) => ({ query: route.query.q }) }
+    {
+      path: '/search',
+      component: SearchUser,
+      props: route => ({ query: route.query.q })
+    }
   ]
 })
 ```