Getters for computed store values in Vue - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a getter that returns the count of items in the store.

Vue

const store = reactive({ items: ['apple', 'banana', 'cherry'] });
const itemCount = computed(() => store.[1].length);

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

Adata

Bcount

Clist

Ditems

Attempts:

3 left

💡 Hint

Common Mistakes

Using a property name that does not exist in the store.

Trying to get length of the store object itself.

The getter accesses the items array in the store to compute its length.

2fill in blank

medium

Complete the code to create a computed getter that returns items filtered by a minimum length.

Vue

const minLength = 6;
const filteredItems = computed(() => store.items.filter(item => item.length [1] minLength));

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

A<

B==

C>=

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using equality operator instead of comparison.

Using less than operator which filters wrong items.

The getter filters items whose length is greater than or equal to the minimum length.

3fill in blank

hard

Fix the error in the computed getter that returns the uppercase version of the first item.

Vue

const firstItemUpper = computed(() => store.items[0].[1]());

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

AtoUpperCase

BupperCase

CtoLowerCase

Duppercase

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect method names like 'uppercase' or 'upperCase'.

Using toLowerCase instead of toUpperCase.

The correct JavaScript string method to convert to uppercase is toUpperCase().

4fill in blank

hard

Fill both blanks to create a getter that returns a map of items with their lengths, filtering only items longer than 5 characters.

Vue

const itemLengths = computed(() =>
  store.items
    .filter(item => item.length [1] 5)
    .map(item => ({ [2]: item, length: item.length }))
);

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

A>

Bitem

C<

Dname

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' in filter condition.

Using an invalid key name in the map object.

The filter uses '>' to select items longer than 5 characters. The map creates objects with the key 'item' holding the item string.

5fill in blank

hard

Fill all three blanks to create a getter that returns an object mapping uppercase item names to their index, only for items with length less than 7.

Vue

const itemIndexMap = computed(() => {
  return store.items
    .map(([1], [2]) => ({ name: [1].toUpperCase(), index: [2] }))
    .filter(obj => obj.name.length [3] 7)
    .reduce((acc, obj) => {
      acc[obj.name] = obj.index;
      return acc;
    }, {});
});

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

Aitem

Bidx

C<

Di

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect parameter names that don't match usage.

Using '>' instead of '<' in the filter condition.

The map function uses item and i as parameters. The filter keeps names with length less than 7.

Practice

1. What is the main purpose of getters in a Vue store?

easy

A. To compute and return derived state based on the store's data

B. To directly modify the store's state values

C. To register new components in the Vue app

D. To handle user input events in components

Solution

1. Step 1: Understand what getters do

   Getters compute values derived from the store's state without changing the state itself.

2. Step 2: Compare options with this role

   Only To compute and return derived state based on the store's data describes computing and returning derived state, which matches getters' purpose.

3. Final Answer:

   To compute and return derived state based on the store's data -> Option A

4. Quick Check:

   Getters compute derived state = B [OK]

Hint: Getters compute data, mutations change data [OK]

Common Mistakes:

• Confusing getters with mutations that modify state
• Thinking getters handle events or components
• Assuming getters register components

2. Which of the following is the correct syntax to define a getter named completedTasks in a Vue store?

easy

A. getters: { completedTasks: function() { return state.tasks.filter(t => t.done) } }

B. getters: { completedTasks: (state) => state.tasks.filter(t => t.done) }

C. getters: { completedTasks() { return this.tasks.filter(t => t.done) } }

D. getters: { completedTasks: (state) => { state.tasks.filter(t => t.done) } }

Solution

1. Step 1: Review correct getter syntax

   A getter is a function receiving state and returning a value. Arrow function with implicit return is common.

2. Step 2: Check each option

   getters: { completedTasks: (state) => state.tasks.filter(t => t.done) } correctly uses an arrow function with state parameter and returns filtered tasks. getters: { completedTasks() { return this.tasks.filter(t => t.done) } } incorrectly uses this which is not available. getters: { completedTasks: function() { return state.tasks.filter(t => t.done) } } lacks state parameter. getters: { completedTasks: (state) => { state.tasks.filter(t => t.done) } } misses return statement.

3. Final Answer:

   getters: { completedTasks: (state) => state.tasks.filter(t => t.done) } -> Option B

4. Quick Check:

   Getter syntax needs state param and return value = C [OK]

Hint: Getters get state as first param and return computed value [OK]

Common Mistakes:

• Using this inside getters instead of state
• Forgetting to return a value from the getter
• Not including state as a parameter

3. Given the Vue store state:

state: { items: [ { id: 1, done: true }, { id: 2, done: false } ] }

and getter:

getters: { doneCount: (state) => state.items.filter(i => i.done).length }

What will store.getters.doneCount return?

medium

A. 2

B. undefined

C. 1

D. 0

Solution

1. Step 1: Analyze the state array

   There are two items: one with done: true and one with done: false.

2. Step 2: Evaluate the getter logic

   The getter filters items where done is true, so only one item matches. Then it returns the length, which is 1.

3. Final Answer:

   1 -> Option C

4. Quick Check:

   Count of done items = 1 [OK]

Hint: Count items with done true using filter and length [OK]

Common Mistakes:

• Counting all items instead of filtered ones
• Returning the filtered array instead of its length
• Assuming undefined because of missing return

4. Identify the error in this Vue store getter definition:

getters: { activeUsers: (state) => { state.users.filter(u => u.active) } }

medium

A. Filter method cannot be used on arrays

B. Incorrect parameter name; should be 'context' instead of 'state'

C. Using arrow function is not allowed for getters

D. Missing return statement inside the getter function

Solution

1. Step 1: Check getter function body

   The getter uses curly braces but does not return the filtered array explicitly.

2. Step 2: Understand arrow function return rules

   When using curly braces in arrow functions, you must use return to output a value. Without it, the function returns undefined.

3. Final Answer:

   Missing return statement inside the getter function -> Option D

4. Quick Check:

   Arrow function with braces needs explicit return = A [OK]

Hint: Arrow functions with braces need explicit return [OK]

Common Mistakes:

• Assuming implicit return with curly braces
• Confusing parameter names for getters
• Thinking filter can't be used on arrays

5. You want a getter that returns the total price of items in a cart, but only for items with quantity > 0.
Given state:

state: { cart: [ { price: 10, quantity: 2 }, { price: 5 }, { price: 3, quantity: 4 } ] }

Which getter correctly computes this total?

hard

A. totalPrice: (state) => state.cart.filter(i => i.quantity > 0).reduce((sum, item) => sum + item.price * item.quantity, 0)

B. totalPrice: (state) => state.cart.reduce((sum, item) => sum + item.price * item.quantity, 0)

C. totalPrice: (state) => state.cart.map(i => i.price * i.quantity).reduce((a, b) => a + b)

D. totalPrice: (state) => state.cart.reduce((sum, item) => sum + item.price, 0)

Solution

1. Step 1: Understand the requirement

   Only items with quantity > 0 should be counted in total price calculation.

2. Step 2: Analyze each option

   totalPrice: (state) => state.cart.reduce((sum, item) => sum + item.price * item.quantity, 0) sums all items regardless of quantity. totalPrice: (state) => state.cart.filter(i => i.quantity > 0).reduce((sum, item) => sum + item.price * item.quantity, 0) filters items with quantity > 0 before summing, which is correct. totalPrice: (state) => state.cart.map(i => i.price * i.quantity).reduce((a, b) => a + b) sums all items including those with zero quantity. totalPrice: (state) => state.cart.reduce((sum, item) => sum + item.price, 0) sums only prices ignoring quantity.

3. Final Answer:

   totalPrice: (state) => state.cart.filter(i => i.quantity > 0).reduce((sum, item) => sum + item.price * item.quantity, 0) -> Option A

4. Quick Check:

   Filter then reduce for quantity > 0 total = A [OK]

Hint: Filter items with quantity > 0 before summing [OK]

Common Mistakes:

• Not filtering out items with zero quantity
• Summing prices without multiplying by quantity
• Using map without filtering first