Shallow ref and shallow reactive in Vue - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a shallow reactive object in Vue.

Vue

import { [1] } from 'vue';

const state = [1]({ count: 0, nested: { value: 10 } });

Drag options to blanks, or click blank then click option'

Aref

Breactive

CshallowRef

DshallowReactive

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'reactive' instead of 'shallowReactive' causes deep reactivity.

Using 'ref' creates a reactive reference, not an object.

Using 'shallowRef' creates a shallow reactive reference, not an object.

Use shallowReactive to create a reactive object where only the root level is reactive, not nested properties.

2fill in blank

medium

Complete the code to create a shallow ref in Vue.

Vue

import { [1] } from 'vue';

const count = [1](0);

Drag options to blanks, or click blank then click option'

AshallowRef

BshallowReactive

Creactive

Dref

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'ref' creates a deep reactive reference.

Using 'reactive' is for objects, not refs.

Using 'shallowReactive' is for objects, not refs.

shallowRef creates a reactive reference where the inner value is not deeply reactive.

3fill in blank

hard

Fix the error in the code to correctly create a shallow reactive object.

Vue

import { [1] } from 'vue';

const data = [1]({ user: { name: 'Alice' } });

Drag options to blanks, or click blank then click option'

AshallowReactive

Breactive

CshallowRef

Dref

Attempts:

3 left

💡 Hint

Common Mistakes

Leaving 'reactive' causes nested properties to be reactive.

Using 'ref' or 'shallowRef' is incorrect for objects.

Replace reactive with shallowReactive to make only the root level reactive.

4fill in blank

hard

Fill both blanks to create a shallow ref and access its value correctly.

Vue

import { [1] } from 'vue';

const count = [1](0);

console.log(count.[2]);

Drag options to blanks, or click blank then click option'

AshallowRef

Bvalue

Ccount

Dref

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'ref' instead of 'shallowRef' changes reactivity depth.

Accessing the ref directly without '.value' causes errors.

Use shallowRef to create the ref and access its inner value with .value.

5fill in blank

hard

Fill all three blanks to create a shallow reactive object and update a nested property.

Vue

import { [1] } from 'vue';

const state = [1]({ nested: { count: 0 } });

state.nested.[2] = 5;

console.log(state.nested.[3]);

Drag options to blanks, or click blank then click option'

AshallowReactive

Bcount

Dreactive

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'reactive' instead of 'shallowReactive' changes reactivity depth.

Using different property names causes undefined errors.

Use shallowReactive to create the object. Then update and access the nested count property.

Practice

1. What does shallowRef in Vue track reactively?

easy

A. All nested properties deeply inside the object

B. Only primitive values inside the object

C. Only changes to the reference itself, not nested properties

D. Changes only to arrays, not objects

Solution

1. Step 1: Understand shallowRef behavior

   shallowRef tracks reactivity only when the reference changes, not inside nested objects.

2. Step 2: Compare with deep reactivity

   Unlike ref or reactive, it does not track nested property changes.

3. Final Answer:

   Only changes to the reference itself, not nested properties -> Option C

4. Quick Check:

   shallowRef tracks reference, not deep changes [OK]

Hint: shallowRef tracks only the outer reference change [OK]

Common Mistakes:

• Thinking shallowRef tracks nested property changes
• Confusing shallowRef with reactive
• Assuming shallowRef tracks primitive values inside

2. Which of the following is the correct way to create a shallow reactive object in Vue?

easy

A. const state = reactive({ count: 0, nested: { value: 1 } })

B. const state = shallowReactive({ count: 0, nested: { value: 1 } })

C. const state = shallowRef({ count: 0, nested: { value: 1 } })

D. const state = ref({ count: 0, nested: { value: 1 } })

Solution

1. Step 1: Identify shallow reactive syntax

   shallowReactive is used to create a shallow reactive object that tracks only top-level properties.

2. Step 2: Differentiate from other APIs

   reactive creates deep reactivity, shallowRef and ref create refs, not shallow reactive objects.

3. Final Answer:

   const state = shallowReactive({ count: 0, nested: { value: 1 } }) -> Option B

4. Quick Check:

   shallowReactive creates shallow reactive objects [OK]

Hint: Use shallowReactive() for shallow reactive objects [OK]

Common Mistakes:

• Using reactive() instead of shallowReactive()
• Confusing shallowRef with shallowReactive
• Using ref() for reactive objects

3. Given the code:

const state = shallowReactive({ count: 0, nested: { value: 1 } });

state.nested.value = 2;
console.log(state.nested.value);

What will be logged to the console?

medium

A. Error: Cannot assign to nested property

B. 1

C. undefined

D. 2

Solution

1. Step 1: Understand shallowReactive behavior

   shallowReactive tracks only top-level properties reactively, but nested objects still exist and can be mutated normally.

2. Step 2: Check nested property assignment

   Assigning state.nested.value = 2 changes the nested object property directly, so the value updates.

3. Final Answer:

   2 -> Option D

4. Quick Check:

   Nested objects update but are not reactive [OK]

Hint: shallowReactive allows nested mutation but no reactivity inside [OK]

Common Mistakes:

• Assuming nested changes are not possible
• Expecting nested changes to trigger reactivity
• Thinking assignment causes error

4. What is the problem with this code snippet?

const state = shallowRef({ count: 0, nested: { value: 1 } });

state.value.nested.value = 5;
console.log(state.value.nested.value);

medium

A. Nested property change won't trigger reactivity

B. Syntax error due to incorrect property access

C. state.value is undefined

D. Cannot assign to nested property inside shallowRef

Solution

1. Step 1: Analyze shallowRef behavior

   shallowRef tracks only changes to the reference itself, not nested properties inside the object.

2. Step 2: Understand nested mutation effect

   Changing state.value.nested.value updates the nested property but does not trigger Vue reactivity updates.

3. Final Answer:

   Nested property change won't trigger reactivity -> Option A

4. Quick Check:

   shallowRef ignores nested property changes [OK]

Hint: shallowRef ignores nested changes, only tracks reference [OK]

Common Mistakes:

• Expecting nested changes to trigger updates
• Confusing shallowRef with reactive
• Thinking this causes syntax or runtime errors

5. You want to optimize performance by tracking only top-level changes in a complex object with nested data. Which approach correctly combines shallow reactivity with a watch to detect nested changes manually?

const state = shallowReactive({ user: { name: 'Alice', age: 30 } });

watch(() => state.user, (newVal, oldVal) => {
  console.log('User changed:', newVal);
});

state.user.name = 'Bob';

What is the expected behavior?

hard

A. The watch callback runs only if state.user is replaced entirely

B. The watch callback runs immediately when state.user.name changes

C. The watch callback will run when state.user.name changes

D. The watch callback runs twice for nested changes

Solution

1. Step 1: Understand shallowReactive and watch

   shallowReactive tracks only top-level properties reactively. The watch on state.user triggers only if the user object reference changes.

2. Step 2: Analyze nested property mutation

   Changing state.user.name mutates a nested property but does not replace the user object, so the watch callback does not run.

3. Final Answer:

   The watch callback runs only if state.user is replaced entirely -> Option A

4. Quick Check:

   shallowReactive watches top-level refs only [OK]

Hint: Watch triggers only on reference changes with shallowReactive [OK]

Common Mistakes:

• Expecting watch to detect nested property changes
• Assuming watch runs on every nested mutation
• Confusing shallowReactive with deep reactive