React Multiple Choice Questions (MCQs) and Answers

Immediately after componentDidMount is called

After the component re-renders

It's available in componentDidMount

None of the above

It directly mutates the state

It may lead to outdated values due to the asynchronous nature of setState

It's the correct way to update state

None of the above

State is not initialized in the constructor

The render method is missing a return statement

The JSX syntax is incorrect

No issue

Props should not be used to set state

componentDidMount should not call setState

No issue

The method is deprecated

Using the onEvent attribute

Using the addEventListener method

Using the handleEvent method

None of the above

this.method = this.method.bind(this) in the constructor

this.method.bind(this) in the render method

Using an arrow function in the method definition

All of the above

To improve performance

To allow access to the 'this' keyword

To prevent memory leaks

To ensure the method is only called once

React events are named using camelCase

React event handlers can return false to prevent default behavior

React wraps the native event into a SyntheticEvent

All of the above

A custom event system for handling native events

A simulation of an event for testing

A deprecated feature for handling events

None of the above

Renders a button that logs 'Click me' when clicked

Renders a clickable button that runs the handleClick method when clicked

Does nothing

Throws an error

By using an arrow function in the onClick attribute

By using the bind method

Both a and b

None of the above

The handleClick method will be called when the component renders, not when the button is clicked

The button will not render

The button will render but will not be clickable

None of the above

The event handler is not bound in the constructor

The event handler attribute should be 'onClick', not 'onclick'

The handleClick method does not exist

No error

'this' is not bound to the component

The method doesn't return anything

The method should be static

No issue

Rendering components based on certain conditions

Rendering components only once

Rendering components without using JSX

None of the above

&& (Logical AND)

|| (Logical OR)

? : (Ternary Operator)

== (Equality)

To perform type checking

To create high-order components

To render one of two components based on a condition

To manipulate state

Return null in the render method

Remove the component from the DOM

Set the component's display style to none

Uninstall the component

if isLoggedIn is true

if isLoggedIn is false

Nothing

An error

Renders if isLoggedIn is true, otherwise

Always renders

Always renders

None of the above

Missing the false condition

isLoggedIn is not defined

is not a valid component

No issue

It will always render

It combines two different conditional rendering patterns incorrectly

will never render

There is no issue; it's a correct implementation

To enhance performance

To uniquely identify list items

To style list items

To handle events on list items

Any unique number

Any string

Any unique identifier

Any type of value can be used as a key

When rendering a list of items

When rendering a single item

When rendering nested components

All of the time

The list will not render

React will throw an error

Performance issues and bugs in the UI update logic

The keys will be automatically generated

$<ul>\{numbers.map(\left(number\right) => <li key=\left\{number\right\}>\left\{number\right\}</li>\left)\right\}</ul>$

$<ul>\{numbers.forEach(\left(number\right) => <li>\left\{number\right\}</li>\left)\right\}</ul>$

$<ul><li>\{numbers.join(\left)\right\}</li></ul>$

$<ul>\{for (let number of numbers) \{<li>\left\{number\right\}</li>\left\}\right\}</ul>$

Use the index of the array

Use a unique property of each item

Any random number

Keys are not necessary in map()

Missing key attribute on $<li>$

Incorrect use of map()

todo.text is undefined

No error

It can cause rendering issues if the list changes

It's not allowed in React

It will make the list render slower

There's no issue with this approach