Nested routes and child views in Vue - Performance & Optimization

Performance: Nested routes and child views

MEDIUM IMPACT

Nested routes affect the rendering speed of views and the complexity of DOM updates when switching between child components.

Rendering nested views in a Vue app using Vue Router

Vue

const routes = [
  {
    path: '/parent',
    component: ParentView,
    children: [
      {
        path: 'child',
        component: () => import('./ChildView.vue') // lazy load child
      }
    ]
  }
];

// In ParentView.vue template
<template>
  <div>
    <router-view /> <!-- renders matched child route -->
  </div>
</template>

Using <router-view> with lazy-loaded child routes defers loading child components until needed, reducing initial bundle size and improving load speed.

📈 Performance GainSaves initial load time by lazy loading child views; reduces memory and DOM nodes until child route is active.

Rendering nested views in a Vue app using Vue Router

Vue

const routes = [
  {
    path: '/parent',
    component: ParentView,
    children: [
      {
        path: 'child',
        component: ChildView
      }
    ]
  }
];

// In ParentView.vue template
<template>
  <div>
    <ChildView /> <!-- directly imported child component -->
  </div>
</template>

Directly importing and rendering child components inside parent without using <router-view> bypasses Vue Router's lazy loading and route management, causing all child components to load upfront.

📉 Performance CostBlocks rendering for all child views on parent load, increasing initial load time and memory usage.

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
Direct child component import inside parent	High (all children mounted upfront)	Multiple reflows on initial load	High paint cost due to many nodes	[X] Bad
Lazy-loaded child routes with <router-view>	Low (children mounted on demand)	Single reflow per route change	Lower paint cost with fewer nodes	[OK] Good

Rendering Pipeline

Nested routes trigger Vue Router to match routes and render components inside <router-view> placeholders. When switching child routes, Vue updates the DOM subtree inside the parent view.

→JavaScript Execution

→DOM Updates

→Paint

→Composite

⚠️ BottleneckDOM Updates due to mounting/unmounting nested child components

Core Web Vital Affected

INP

Nested routes affect the rendering speed of views and the complexity of DOM updates when switching between child components.

Optimization Tips

1Use <router-view> to render nested child routes instead of direct component imports.

2Lazy load child route components to reduce initial bundle size and improve load speed.

3Avoid very deep nesting to minimize DOM complexity and reflow costs.

Performance Quiz - 3 Questions

What is a main performance benefit of using lazy-loaded child routes in Vue?

A Ensures all child components load immediately for faster navigation

B Reduces initial bundle size and delays loading child views until needed

C Increases DOM nodes to improve rendering speed

D Prevents any reflows during route changes

DevTools: Performance

How to check: Record a performance profile while navigating nested routes; look for long scripting and rendering times during route changes.

What to look for: Check for multiple reflows and long scripting tasks when child views mount; fewer and shorter tasks indicate better performance.

Practice

1. What is the main purpose of nested routes in Vue Router?

easy

A. To load multiple Vue apps on the same page

B. To display child views inside a parent view using <router-view />

C. To create routes without components

D. To disable navigation guards

Solution

1. Step 1: Understand nested routes concept

   Nested routes allow smaller views (child views) to be shown inside bigger views (parent views).

2. Step 2: Identify how child views are displayed

   Child views appear inside the parent component where <router-view /> is placed.

3. Final Answer:

   To display child views inside a parent view using <router-view /> -> Option B

4. Quick Check:

   Nested routes = child views inside parent with <router-view /> [OK]

Hint: Nested routes show child views inside parents with [OK]

Common Mistakes:

• Thinking nested routes load separate apps
• Believing nested routes don't need
• Confusing nested routes with route guards

2. Which of the following is the correct way to define a child route inside a parent route in Vue Router?

easy

A. { path: '/parent', component: Parent, children: [{ path: 'child', component: Child }] }

B. { path: '/parent/child', component: Child }

C. { path: '/parent', component: Parent, child: [{ path: 'child', component: Child }] }

D. { path: '/parent', component: Parent, children: { path: 'child', component: Child } }

Solution

1. Step 1: Recall Vue Router child route syntax

   Child routes go inside a children array property of the parent route object.

2. Step 2: Check each option's structure

   { path: '/parent', component: Parent, children: [{ path: 'child', component: Child }] } correctly uses children: [{ path: 'child', component: Child }]. Options C and D use wrong keys or types. { path: '/parent/child', component: Child } defines a separate route, not nested.

3. Final Answer:

   { path: '/parent', component: Parent, children: [{ path: 'child', component: Child }] } -> Option A

4. Quick Check:

   Child routes = inside children array [OK]

Hint: Child routes go inside a children array in parent route [OK]

Common Mistakes:

• Using 'child' instead of 'children' key
• Defining child routes outside parent route
• Using object instead of array for children

3. Given this route config and components, what will be rendered when navigating to /dashboard/settings?

const routes = [
  { path: '/dashboard', component: Dashboard, children: [
    { path: 'settings', component: Settings }
  ]}
];

// Dashboard.vue template:
// 
Dashboard

// Settings.vue template:
// 
Settings Page

medium

A. Nothing renders due to missing

B. Settings Page

C. DashboardSettings Page

D. Dashboard

Solution

1. Step 1: Understand nested route rendering

   When visiting '/dashboard/settings', Vue renders Dashboard component first, then inside its <router-view /> renders Settings component.

2. Step 2: Combine rendered HTML from both components

   Dashboard shows <h1>Dashboard</h1> and Settings shows <h2>Settings Page</h2>. Both appear together.

3. Final Answer:

   <h1>Dashboard</h1><h2>Settings Page</h2> -> Option C

4. Quick Check:

   Nested route renders parent + child views [OK]

Hint: Nested routes render parent plus child inside [OK]

Common Mistakes:

• Expecting only child component to render
• Forgetting in parent
• Confusing full path with child path

4. What is wrong with this route configuration if child views do not appear?

const routes = [
  { path: '/profile', component: Profile, children: [
    { path: 'edit', component: EditProfile }
  ]}
];

// Profile.vue template:
// 
Profile Page

medium

A. Profile.vue is missing to display child routes

B. Child route path should start with '/'

C. Children array should be outside the parent route object

D. EditProfile component must be imported inside Profile.vue

Solution

1. Step 1: Check how child routes display

   Child routes render inside the parent's <router-view />. Without it, child views won't show.

2. Step 2: Inspect Profile.vue template

   Profile.vue only has <h1>Profile Page</h1> and no <router-view />, so child routes can't render.

3. Final Answer:

   Profile.vue is missing <router-view /> to display child routes -> Option A

4. Quick Check:

   Missing <router-view /> = no child views [OK]

Hint: Parent needs to show child routes [OK]

Common Mistakes:

• Adding '/' at start of child path incorrectly
• Placing children outside parent route object
• Assuming child component imports affect rendering

5. You want to create a nested route where /shop shows a Shop component and /shop/products shows a Products component inside Shop. Which setup correctly achieves this and ensures accessibility and responsiveness? A) Define routes with children array, use <router-view /> in Shop, and add ARIA roles and responsive CSS. B) Define separate routes for /shop and /shop/products without nesting, and use CSS media queries only. C) Use nested routes but omit <router-view /> in Shop and rely on v-if to show Products. D) Use nested routes with children but place <router-view /> outside Shop component.

hard

A. Use nested routes but place outside Shop component

B. Define separate routes without nesting and use only CSS media queries

C. Use nested routes but omit in Shop and use v-if for Products

D. Define routes with children array, use in Shop, add ARIA roles and responsive CSS

Solution

1. Step 1: Setup nested routes properly

   Use a children array in the /shop route to define /shop/products as a child route.

2. Step 2: Ensure Shop component includes <router-view />

   This allows Products component to render inside Shop when navigating to /shop/products.

3. Step 3: Add accessibility and responsiveness

   Use ARIA roles for landmarks and semantic HTML, plus responsive CSS (like Flexbox or Grid) to adapt layout on different screens.

4. Final Answer:

   Define routes with children array, use <router-view /> in Shop, add ARIA roles and responsive CSS -> Option D

5. Quick Check:

   Nested routes + router-view + accessibility + responsive CSS = Define routes with children array, use in Shop, add ARIA roles and responsive CSS [OK]

Hint: Nested routes need router-view in parent plus ARIA and responsive CSS [OK]

Common Mistakes:

• Omitting router-view in parent component
• Not adding ARIA roles for accessibility
• Ignoring responsive design in CSS
• Placing router-view outside parent component