Keep-alive for caching components in Vue - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the component in Vue?

The component caches inactive Vue components, preserving their state and avoiding re-rendering when they are switched back into view.

beginner

How do you wrap components to enable caching with ?

You wrap dynamic components or router views inside tags, like <component :is="currentView" />.

intermediate

What props can you use with to control which components are cached?

You can use include and exclude props with component names to specify which components to cache or ignore.

intermediate

What lifecycle hooks are triggered when a component is cached and then activated again?

When cached, the component's deactivated hook runs when hidden, and activated runs when it becomes active again.

beginner

Why is useful for improving user experience in Vue apps?

It speeds up navigation by reusing component state and DOM, reducing loading time and preserving user input or scroll position.

What does the component do in Vue?

A Automatically reloads components on every render

B Removes components from the DOM permanently

C Caches inactive components to preserve their state

D Converts components into plain HTML

caches inactive components so they keep their state and don't re-render unnecessarily.

Which prop of lets you specify components to cache?

A include

B exclude

C cache

D preserve

The include prop specifies which component names to cache inside .

Which lifecycle hook runs when a cached component becomes active again?

A mounted

B activated

C created

D deactivated

The activated hook runs when a cached component is reactivated and shown again.

How do you use with dynamic components?

A Wrap the dynamic component inside <keep-alive> tags

B Add a cache attribute to the component

C Use a special caching plugin

D No special action is needed

You wrap dynamic components inside to cache them when inactive.

What benefit does provide to user experience?

A Slower navigation but better visuals

B Removes all component data on switch

C Automatically fixes bugs in components

D Preserves component state and speeds up navigation

preserves state and DOM, making navigation faster and smoother for users.

Explain how works in Vue and why you would use it.

Think about how to keep a component's data and appearance when switching views.

Describe the lifecycle hooks related to and their roles.

Focus on what happens when a cached component hides and shows.

Practice

1. What is the main purpose of the <keep-alive> component in Vue?

easy

A. To cache components and preserve their state when switching views

B. To permanently remove components from the DOM

C. To reload components every time they are displayed

D. To style components with CSS automatically

Solution

1. Step 1: Understand what <keep-alive> does

   The <keep-alive> component caches inactive components instead of destroying them.

2. Step 2: Identify the effect on component state

   Because components are cached, their state (like user input or scroll position) is preserved when switching back.

3. Final Answer:

   To cache components and preserve their state when switching views -> Option A

4. Quick Check:

   Keep-alive caches components [OK]

Hint: Remember: keep-alive means keep the component's state alive [OK]

Common Mistakes:

• Thinking keep-alive reloads components every time
• Confusing keep-alive with styling or layout features
• Assuming keep-alive removes components permanently

2. Which of the following is the correct syntax to use keep-alive with a dynamic component named MyComponent?

easy

A. <keep-alive><component :is="MyComponent" /></keep-alive>

B. <keep-alive :is="MyComponent" />

C. <component :is="MyComponent" keep-alive />

D. <keep-alive><MyComponent /></keep-alive>

Solution

1. Step 1: Recall how to wrap dynamic components with keep-alive

   The <keep-alive> component wraps around a dynamic component using <component :is="..." />.

2. Step 2: Check each option's syntax

   <keep-alive><component :is="MyComponent" /></keep-alive> correctly wraps <component :is="MyComponent" /> inside <keep-alive>. Options A and C misuse attributes or tags. <keep-alive><MyComponent /></keep-alive> tries to wrap a component tag directly, which is invalid for dynamic components.

3. Final Answer:

   <keep-alive><component :is="MyComponent" /></keep-alive> -> Option A

4. Quick Check:

   Wrap dynamic component inside keep-alive [OK]

Hint: Wrap inside tags [OK]

Common Mistakes:

• Trying to add keep-alive as a prop to component
• Using component tags directly without :is for dynamic components
• Placing :is on keep-alive instead of component

3. Given this Vue template:

<keep-alive>
  <component :is="currentView" />
</keep-alive>

and currentView switches between 'ViewA' and 'ViewB'. What happens to the state of 'ViewA' when switching to 'ViewB' and back?

medium

A. The state of 'ViewA' is reset to initial values

B. 'ViewA' state is preserved because it is cached

C. An error occurs because keep-alive cannot cache dynamic components

D. 'ViewA' is destroyed and recreated fresh

Solution

1. Step 1: Understand keep-alive behavior with dynamic components

   When wrapped in <keep-alive>, inactive components are cached, not destroyed.

2. Step 2: Apply this to switching views

   Switching from 'ViewA' to 'ViewB' caches 'ViewA'. Returning to 'ViewA' restores its previous state.

3. Final Answer:

   'ViewA' state is preserved because it is cached -> Option B

4. Quick Check:

   Keep-alive caches dynamic components [OK]

Hint: Switching views inside keep-alive preserves previous state [OK]

Common Mistakes:

• Assuming components reset on every switch
• Thinking keep-alive destroys inactive components
• Believing keep-alive causes runtime errors with dynamic components

4. What is wrong with this code snippet?

<keep-alive>
  <MyComponent :is="currentView" />
</keep-alive>

Assuming currentView is a string with component name.

medium

A. keep-alive cannot wrap components

B. Missing closing tag for keep-alive

C. currentView should be a component object, not a string

D. Using :is on a component tag instead of <component>

Solution

1. Step 1: Identify correct usage of dynamic components

   Dynamic components require the <component :is="..." /> syntax, not <MyComponent :is="..." />.

2. Step 2: Check the code snippet

   The snippet incorrectly uses :is on a named component tag, which is invalid and causes errors.

3. Final Answer:

   Using :is on a component tag instead of <component> -> Option D

4. Quick Check:

   Dynamic components need <component :is> syntax [OK]

Hint: Use for dynamic components, not named tags [OK]

Common Mistakes:

• Placing :is on a named component tag
• Forgetting to close keep-alive tags
• Thinking keep-alive cannot wrap components

5. You want to cache only the 'UserProfile' component but not 'UserSettings' when switching views. Which is the correct way to use <keep-alive> with the include prop to achieve this?

hard

A. <keep-alive include={UserProfile}><component :is="currentView" /></keep-alive>

B. <keep-alive exclude="UserProfile"><component :is="currentView" /></keep-alive>

C. <keep-alive include="UserProfile"><component :is="currentView" /></keep-alive>

D. <keep-alive include="UserSettings"><component :is="currentView" /></keep-alive>

Solution

1. Step 1: Understand the include prop on keep-alive

   The include prop accepts a string or array of component names to cache only those components.

2. Step 2: Apply include to cache 'UserProfile' only

   Setting include="UserProfile" caches only the 'UserProfile' component and excludes others like 'UserSettings'.

3. Final Answer:

   <keep-alive include="UserProfile"><component :is="currentView" /></keep-alive> -> Option C

4. Quick Check:

   Use include="UserProfile" to cache only that component [OK]

Hint: Use include prop with component name to cache selectively [OK]

Common Mistakes:

• Using exclude instead of include to cache desired component
• Passing include as an object instead of string
• Including wrong component name in include prop