Readonly for immutable reactive data in Vue - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the readonly function do in Vue?

It creates a reactive object that cannot be changed. Any attempt to modify it will fail silently or warn in development mode.

beginner

Why use readonly instead of reactive in Vue?

Use readonly to protect data from accidental changes while still allowing Vue to track dependencies and update the UI.

intermediate

How does Vue behave if you try to modify a readonly reactive object?

Vue will not update the object and will warn you in the console during development to prevent accidental mutations.

intermediate

Can you nest readonly objects inside other reactive objects in Vue?

Yes, nested objects inside a readonly object are also made readonly recursively.

beginner

Give a simple example of creating a readonly reactive object in Vue.

Example:<br><pre>import { reactive, readonly } from 'vue';
const state = reactive({ count: 0 });
const readOnlyState = readonly(state);</pre><br>This makes <code>readOnlyState</code> immutable but reactive.

What happens if you try to change a property on a Vue readonly object?

A The change updates the object normally.

B The change is ignored and a warning appears in development mode.

C Vue throws a runtime error and crashes.

D The object becomes reactive and mutable.

Readonly objects prevent changes and warn you during development to avoid accidental mutations.

Which Vue function creates an immutable reactive object?

A computed()

B reactive()

C ref()

D readonly()

readonly() creates a reactive object that cannot be changed.

Can a readonly object still trigger UI updates in Vue?

A Only if you convert it back to reactive.

B No, it does not trigger updates.

C Yes, because it is reactive but immutable.

D Only if you use <code>ref()</code> with it.

Readonly objects are reactive, so Vue tracks dependencies and updates the UI when underlying data changes.

What is a common use case for readonly in Vue?

A To share state safely without allowing changes.

B To make data editable by the user.

C To create computed properties.

D To watch for changes manually.

readonly is used to share state that should not be changed by consumers.

If you have a nested object inside a readonly object, what happens to the nested object?

A It is also made readonly recursively.

B It remains mutable.

C It becomes reactive but writable.

D It is ignored by Vue's reactivity system.

Vue applies readonly recursively to nested objects to keep immutability consistent.

Explain how Vue's readonly function helps manage immutable reactive data.

Think about protecting data while keeping UI updates.

Describe a scenario where using readonly in Vue is better than using reactive.

Consider teamwork where some members only view data.