POST requests for form submission in Vue - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What happens when this Vue component submits the form?

Consider this Vue 3 component using the Composition API. What will be the console output after submitting the form?

Vue

<template>
  <form @submit.prevent="submitForm">
    <input v-model="username" placeholder="Username" />
    <button type="submit">Submit</button>
  </form>
</template>

<script setup>
import { ref } from 'vue'

const username = ref('')

async function submitForm() {
  const response = await fetch('/api/login', {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify({ username: username.value })
  })
  const data = await response.json()
  console.log(data.message)
}
</script>

A Logs undefined because username is not reactive

B Throws a syntax error because fetch is used incorrectly

C Logs the server response message if the POST is successful

D Prevents form submission but does not send any request

💡 Hint

Look at how username is used and how fetch is called with await.

The component uses ref to make username reactive. The submitForm function sends a POST request with JSON body and logs the server's response message.

📝 Syntax

intermediate

Which option correctly sends a POST request with JSON body in Vue?

Choose the code snippet that correctly sends a POST request with JSON data inside a Vue method.

A fetch('/api/data', { method: 'POST', body: JSON.stringify({ name: 'Alice' }) })

B fetch('/api/data', { method: 'POST', headers: { 'Content-Type': 'application/json' }, body: JSON.stringify({ name: 'Alice' }) })

C fetch('/api/data', { method: 'POST', headers: { 'Content-Type': 'text/plain' }, body: { name: 'Alice' } })

D fetch('/api/data', { method: 'POST', headers: { 'Content-Type': 'application/json' }, body: { name: 'Alice' } })

💡 Hint

Remember to set the correct Content-Type header and stringify the body.

Option B correctly sets the header to application/json and stringifies the body. Options C and D send the body as an object, which is invalid. Option B misses the header.

🔧 Debug

advanced

Why does this Vue POST request fail with a CORS error?

This Vue component sends a POST request to an external API but gets a CORS error in the browser. What is the most likely cause?

Vue

<script setup>
import { ref } from 'vue'
const data = ref('')
async function sendData() {
  const res = await fetch('https://external.api/submit', {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify({ data: data.value })
  })
  console.log(await res.json())
}
</script>

A The external API does not allow cross-origin POST requests from this domain

B The fetch call is missing the 'mode' option set to 'cors'

C Vue's reactivity system blocks cross-origin requests

D The JSON body is not stringified properly

💡 Hint

Think about browser security rules for cross-origin requests.

CORS errors happen when the server does not permit requests from your site. The client code is correct; the server must allow the origin.

❓ state_output

advanced

What is the value of 'status' after submitting this form?

In this Vue component, what will be the value of status after the form is submitted and the server responds with { success: true }?

Vue

<template>
  <form @submit.prevent="submit">
    <input v-model="input" />
    <button type="submit">Send</button>
  </form>
  <p>{{ status }}</p>
</template>

<script setup>
import { ref } from 'vue'
const input = ref('')
const status = ref('idle')

async function submit() {
  status.value = 'sending'
  const res = await fetch('/api/send', {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify({ input: input.value })
  })
  const data = await res.json()
  if (data.success) {
    status.value = 'success'
  } else {
    status.value = 'error'
  }
}
</script>

A 'idle'

B 'sending'

C 'error'

D 'success'

💡 Hint

Look at how status changes after the fetch call.

The code sets status to 'sending' before the request, then updates it to 'success' if the server responds with { success: true }.

🧠 Conceptual

expert

Why use async/await with POST requests in Vue form submission?

Which is the best explanation for using async/await when sending POST requests in Vue form submission?

A It allows writing asynchronous code in a readable way and waits for the server response before proceeding

B It automatically retries the POST request if it fails

C It blocks the UI thread until the request finishes, preventing user interaction

D It converts the POST request into a synchronous call to improve performance

💡 Hint

Think about how async/await affects code flow and readability.

Async/await lets you write asynchronous code that looks like normal sequential code. It waits for the fetch to complete before moving on, improving clarity.