JavaScript quiz

Test your JavaScript knowledge with a free interactive quiz — 104 questions with answers and explanations. No signup needed to play.

In a subclass constructor, what must be called before using `this`?

1. In a subclass constructor, what must be called before using `this`?
2. What does `extends` do in a class declaration?
3. Which method converts a JSON string into a JavaScript object?
4. What is the result of `Boolean("")`?
5. What is hoisting in JavaScript?
6. What is the key difference between `??` and `||`?
7. Which array method creates a new array with all elements that pass a test function?
8. What does the `this` keyword refer to inside a regular function called in the global scope in non-strict mode?
9. What can an ES module have more than one of?
10. Which of these correctly creates an object using shorthand property notation (ES6)?
11. Which statement is used to handle exceptions in JavaScript?
12. What does the spread operator `...` do when used with an array?

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