JavaScript and React Quiz

What is the output of the following code: var x = 1; function foo() { var x = 2; function bar() { console.log(x); } return bar; } var baz = foo(); baz();

• 1

• 2

• undefined

• Error

What is the output of the following code: var x = [1, 2, 3]; var y = x.slice(1); console.log(y);

• [1, 2]

• [2, 3]

• [1, 3]

• Error

What is the output of the following code: var x = 5; console.log(++x);

• 5

• 6

• NaN

• Error

What is the output of the following code: var x = true; var y = false; console.log(x || y);

• true

• false

• null

• Error

What is the output of the following code: console.log(typeof null);

• "null"

• "object"

• "undefined"

• Error

What is React.js?

• A JavaScript framework

• A JavaScript library for building user interfaces

• A CSS library

• A database

Who developed React.js?

• Google

• Microsoft

• Facebook

• Apple

What is the virtual DOM in React?

• A copy of the real DOM that is synced with it

• The actual DOM

• A separate database for React components

• A component tree manager

Which hook is used to handle state in a functional component?

• useReducer

• useEffect

• useState

• useMemo

What is JSX?

• A database language

• JavaScript XML

• A CSS preprocessor

• A testing library