React Forms and Events

Question 1

What makes a form input 'controlled' in React?

Accepted Answer

Its value is managed by React state

Answer

It has a `name` attribute

Answer

It uses the `ref` attribute

Answer

It has an `autoFocus` prop

Question 2

How do you prevent a form's default submission behavior in React?

Accepted Answer

Call `event.preventDefault()` in the onSubmit handler

Answer

Set `type='button'` on the submit button

Answer

Add a `noSubmit` attribute to the form

Answer

Call `event.stopPropagation()` in the handler

Question 3

For a checkbox input, which property gives you the boolean checked state in an onChange handler?

Accepted Answer

event.target.checked

Answer

event.target.value

Answer

event.target.data

Answer

event.target.state

Question 4

What is the recommended pattern for handling multiple controlled inputs with a single onChange handler?

Accepted Answer

Use event.target.name to identify the input and update the corresponding state key

Answer

Use event.target.id to identify the input and update state

Answer

Create separate state variables and handlers for each input

Answer

Use refs for each input and read them on submit

Question 5

What is an 'uncontrolled' component in React?

Accepted Answer

A component where the DOM manages its own form data internally

Answer

A component that lacks event handlers

Answer

A component without lifecycle methods

Answer

A component that uses Context instead of props

Question 6

What does the `defaultValue` prop do on a React input element?

Accepted Answer

Sets the initial value without making the input controlled

Answer

Sets placeholder text shown when the field is empty

Answer

Makes the input required for form submission

Answer

Disables user editing of the input

Question 7

Which React event fires when the value of an input, textarea, or select element changes?

Accepted Answer

onChange

Answer

onInput

Answer

onModify

Answer

onUpdate