Blookly trắc nghiệm 9 - Phan Thủy

What is the result of the typeof NaN expression in JavaScript?

• A. undefined

• B.number

• C. object

• D.NaN

Which of the following methods is used to convert a string to an integer?

• A. Number()

• B. parseInt()

• C. parseFloat()

• D. toFixed()

What is the result of the expression [1, 2, 3].map(x => x * 2) in JavaScript?

• A. [2, 4, 6]

• B. [1, 2, 3]

• C. 6

• D. [2, 3, 4]

How to create an object that inherits from another object in JavaScript?

• A. Object.inherit()

• B. Object.create()

• C. Object.derive()

• D. Object.extend()

In JavaScript, what does the this keyword in an object's method refer to?

• A. Global object

• B. Current object

• C. Parent object

• D. Child object

What is the result of the expression "5" - 3 in JavaScript?

• A. 2

• B. 53

• C.NaN

• D. Error

Which of the following methods is used to merge arrays in JavaScript?

• A. concat()

• B. push()

• C. merge()

• D. combine()

What is the result of the expression 'Hello'.charAt(1) in JavaScript?

• A.H

• B. e

• C.l

• D.o

In JavaScript, which keyword is used to declare a constant?

• A. var

• B. let

• C. const

• D. constant

Which of the following methods is used to check whether an array contains a particular element?

• A.has()

• B. includes()

• C. contains()

• D. exists()