JavaScript ES6+ Features

Q: Is the JavaScript ES6+ Features quiz free?

Yes. The JavaScript ES6+ Features quiz is completely free with no signup. Answer the questions, get instant scoring, and earn XP as you go.

Q: What level is the JavaScript ES6+ Features quiz?

This is a Medium-level quiz. Each question includes the correct answer so you learn as you test yourself, whatever your starting point.

Q: How can I prepare for this quiz?

Review the linked courses and notes for the topic first, then take the quiz to check your understanding. You can retake it anytime to track improvement.

Question 1

What does array destructuring `const [a, b] = [1, 2, 3]` assign to `a` and `b`?

Accepted Answer

Destructuring assigns array elements positionally. `a` gets the first element (1), `b` gets the second (2). The third element (3) is ignored.

Question 2

What is the spread operator used for in `const merged = [...arr1, ...arr2]`?

Accepted Answer

The spread operator (`...`) expands an iterable (array, string, etc.) into individual elements. Here it creates a new array combining all elements of `arr1` and `arr2`.

Question 3

A Promise in JavaScript can only be in one of three states: pending, fulfilled, or rejected.

Accepted Answer

True. Promises start as `pending`, then either `fulfilled` (resolved with a value) or `rejected` (with a reason/error). Once settled, a Promise state cannot change.

Question 4

What does the `await` keyword do inside an `async` function?

Accepted Answer

`await` pauses the execution of an async function until the Promise settles. It unwraps the resolved value, making async code read like synchronous code.

Question 5

What is the key difference between `Map` and a plain object in JavaScript?

Accepted Answer

`Map` maintains insertion order, allows any value (including objects) as keys, has a `.size` property, and is iterable. Plain objects have string/symbol keys only.

Question 6

Which syntax correctly imports a default export from a module?

Accepted Answer

Default exports are imported without curly braces. Named exports use `{ }`. `import * as X from "..."` imports all named exports as properties of X.

Question 7

Optional chaining (`?.`) throws an error if the property does not exist.

Accepted Answer

False. Optional chaining (`?.`) short-circuits and returns `undefined` instead of throwing a TypeError when accessing a property on `null` or `undefined`.

Question 8

What does the nullish coalescing operator (`??`) do?

Accepted Answer

`??` returns its right-hand operand only when the left is `null` or `undefined`. Unlike `||`, it does NOT treat `0`, `""`, or `false` as nullish.

Question 9

What does `Set` guarantee about its values?

Accepted Answer

A `Set` is a collection of unique values. Duplicate entries are automatically ignored. It is useful for deduplicating arrays: `[...new Set(arr)]`.

Question 10

`Symbol()` always creates a unique value, even if two Symbols are created with the same description.

Accepted Answer

True. Every `Symbol()` call produces a guaranteed unique value. `Symbol("id") === Symbol("id")` is `false`. Symbols are often used as unique object property keys.

JavaScript ES6+ Features

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JavaScript ES6+ Features

Frequently Asked Questions

Is the JavaScript ES6+ Features quiz free?

What level is the JavaScript ES6+ Features quiz?

How can I prepare for this quiz?

Learn the Topic

JavaScript ES6 Cheatsheet

JS Promises & Async/Await

Go deeper on this topic