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Medium Free Computer & Technology JavaScript

JavaScript Quiz

Check your understanding of JavaScript from basic syntax to the concepts used in modern web applications.

30 Questions
30 min Duration
50% To pass
1.00 Marks / correct

Instructions

  • This quiz has 30 questions.
  • Questions are picked at random from a bank of 99, so each attempt is different.
  • You have 30 minutes. The quiz submits automatically when time runs out.
  • You need 50% to pass.
  • There is no negative marking.
  • You can mark questions for review and return to them before submitting.
  • Correct answers and explanations are shown after you submit.

Sample Questions & Answers

A preview of 12 questions from this quiz, each with the correct answer and a written explanation. Attempt the full, timed quiz to be scored and earn XP.

  1. Question 1

    Which keyword declares a block-scoped variable that can be reassigned in JavaScript?

    • var
    • let Correct answer
    • const
    • static
    Explanation: The let keyword declares a block-scoped variable whose value can later be reassigned.
  2. Question 2

    Which keyword declares a block-scoped variable that cannot be reassigned?

    • var
    • let
    • const Correct answer
    • define
    Explanation: The const keyword creates a block-scoped binding that cannot be reassigned.
  3. Question 3

    Which operator checks both value and type equality in JavaScript?

    • ==
    • =
    • === Correct answer
    • !==
    Explanation: The strict equality operator === compares both the value and the type without coercion.
  4. Question 4

    Which method converts a JavaScript object into a JSON string?

    • JSON.parse()
    • JSON.stringify() Correct answer
    • JSON.object()
    • JSON.encode()
    Explanation: JSON.stringify() serializes a JavaScript value into a JSON-formatted string.
  5. Question 5

    Which method parses a JSON string into a JavaScript value?

    • JSON.parse() Correct answer
    • JSON.stringify()
    • JSON.decode()
    • JSON.toObject()
    Explanation: JSON.parse() converts valid JSON text into the corresponding JavaScript value.
  6. Question 6

    Which array method adds one or more elements to the end of an array?

    • shift()
    • unshift()
    • push() Correct answer
    • append()
    Explanation: The push() method adds elements to the end of an array and returns its new length.
  7. Question 7

    Which array method removes the last element from an array?

    • pop() Correct answer
    • shift()
    • removeLast()
    • spliceEnd()
    Explanation: The pop() method removes and returns the last element of an array.
  8. Question 8

    Which array method removes the first element from an array?

    • pop()
    • shift() Correct answer
    • unshift()
    • slice()
    Explanation: The shift() method removes and returns the first element of an array.
  9. Question 9

    Which array method adds elements to the beginning of an array?

    • push()
    • prepend()
    • unshift() Correct answer
    • shift()
    Explanation: The unshift() method adds one or more elements to the beginning of an array.
  10. Question 10

    What does typeof null return in JavaScript?

    • null
    • undefined
    • object Correct answer
    • boolean
    Explanation: Due to a historical behavior in JavaScript, typeof null returns the string object.
  11. Question 11

    What is the result of typeof undefined?

    • null
    • undefined Correct answer
    • void
    • object
    Explanation: The typeof operator returns the string undefined for the primitive value undefined.
  12. Question 12

    Which value represents a number that is not a valid numeric result?

    • Infinity
    • NaN Correct answer
    • null
    • undefined
    Explanation: NaN means Not-a-Number and represents an invalid or unrepresentable numeric result.

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Explore more: All Computer & Technology quizzes · JavaScript

JavaScript Practice

JavaScript is one of the core technologies used on the web. This quiz gives you a chance to revise language fundamentals and the concepts that frequently appear while learning front-end or full-stack development.

Frequently Asked Questions

Each attempt serves 30 questions, drawn at random from a bank of 99, with 30 minutes.

You need at least 50% to pass this quiz.

No, there is no negative marking on this quiz.

Yes. You can attempt this quiz again at any time, though first-attempt XP bonuses apply only once.

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