Composable accepting parameters in Vue - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this Vue composable usage?

Consider this composable that accepts a parameter and returns a reactive value:

import { ref } from 'vue'

export function useCounter(start) {
  const count = ref(start)
  function increment() {
    count.value++
  }
  return { count, increment }
}

In a component, we use it like this:

const { count, increment } = useCounter(5)
increment()
increment()
console.log(count.value)

What will be logged?

Vue

import { ref } from 'vue'

export function useCounter(start) {
  const count = ref(start)
  function increment() {
    count.value++
  }
  return { count, increment }
}

const { count, increment } = useCounter(5)
increment()
increment()
console.log(count.value)

A 7

B undefined

C 2

D 5

💡 Hint

Think about how many times increment() is called and what count starts at.

The composable useCounter starts the count at 5. Each call to increment() adds 1. Called twice, count becomes 7.

📝 Syntax

intermediate

Which option correctly defines a composable accepting a parameter?

Which of these Vue composable definitions correctly accepts a parameter initialValue and returns a reactive value initialized with it?

A

export function useValue(initialValue) {
  const value = ref(initialValue)
  return { value }
}

B

export function useValue(initialValue) {
  const value = reactive(initialValue)
  return value
}

C

export function useValue() {
  const value = ref(initialValue)
  return { value }
}

D

export function useValue(initialValue) {
  const value = ref()
  value = initialValue
  return { value }
}

💡 Hint

Remember to initialize ref with the parameter and return it properly.

Option A correctly takes initialValue as parameter, initializes value with ref(initialValue), and returns it inside an object.

Option A uses initialValue without parameter, causing error.

Option A uses reactive on a primitive, which is incorrect.

Option A tries to assign to a const variable, causing error.

🔧 Debug

advanced

Why does this composable not update the reactive value?

Look at this composable:

import { ref } from 'vue'

export function useToggle(initial) {
  let state = ref(initial)
  function toggle() {
    state = !state
  }
  return { state, toggle }
}

When used, calling toggle() does not update state.value. Why?

Vue

import { ref } from 'vue'

export function useToggle(initial) {
  let state = ref(initial)
  function toggle() {
    state = !state
  }
  return { state, toggle }
}

A Because the function toggle is not called properly

B Because ref cannot hold boolean values

C Because the toggle function assigns a boolean to the ref variable instead of updating state.value

D Because the initial parameter is not reactive

💡 Hint

Check how the toggle function changes state.

The toggle function assigns a boolean directly to state, replacing the ref object. It should update state.value instead.

❓ state_output

advanced

What is the value of count after this composable usage?

Given this composable:

import { ref } from 'vue'

export function useStepCounter(start, step) {
  const count = ref(start)
  function advance() {
    count.value += step
  }
  return { count, advance }
}

And this usage:

const { count, advance } = useStepCounter(10, 3)
advance()
advance()
advance()
console.log(count.value)

What is logged?

Vue

import { ref } from 'vue'

export function useStepCounter(start, step) {
  const count = ref(start)
  function advance() {
    count.value += step
  }
  return { count, advance }
}

const { count, advance } = useStepCounter(10, 3)
advance()
advance()
advance()
console.log(count.value)

A 13

B 19

C 10

D undefined

💡 Hint

Count starts at 10 and increases by 3 each advance call.

Starting at 10, three advances add 3 each: 10 + 3 + 3 + 3 = 19.

🧠 Conceptual

expert

Why pass parameters to a composable instead of hardcoding values?

In Vue, why is it better to pass parameters to a composable function rather than hardcoding values inside it?

A Hardcoding values prevents accidental changes to reactive state

B Hardcoding values improves performance by avoiding parameter parsing

C Parameters are required to make the composable reactive

D Passing parameters makes the composable reusable with different data and easier to test

💡 Hint

Think about reusability and flexibility.

Passing parameters allows the composable to work with different inputs, making it reusable and easier to test. Hardcoding limits flexibility.