Question 1

What’s the difference between `map()` and `filter()`?

Accepted Answer

`map()` transforms each array element and returns a new array of the same length, while `filter()` keeps only elements that pass a test, possibly shortening the array. I use `map` for conversions and `filter` for selection.

Question 2

How do you generate a random number in JavaScript?

Accepted Answer

Use `Math.random()` for a number between 0 and 1, then scale it—like `Math.floor(Math.random() * max)` for integers. It’s simple and built-in. I use it for games or random selections.

Question 3

How do you remove duplicates from an array?

Accepted Answer

You can remove duplicates with `Set`—like `([...new Set(arr)])`—since Sets only store unique values. It’s quick and clean, though it doesn’t preserve order in older browsers. I use it unless I need something fancier.

Question 4

How do you find the maximum value in an array?

Accepted Answer

You can use `Math.max()` with the spread operator—like `Math.max(...arr)`—to find the highest value. `reduce()` works too but is overkill for this. I go with `Math.max()` for its simplicity.

Question 5

How do you destructure an object?

Accepted Answer

Destructuring pulls properties from an object into variables using `{ prop } = obj`. It’s concise and great for cleaner code. I use it to grab what I need without dot notation everywhere.

Question 6

How do you implement a stack in JavaScript?

Accepted Answer

A stack is a LIFO structure—you can use an array with `push()` and `pop()`. It’s simple and built-in, though you could write a class for more control. I use arrays for quick stacks in algorithms.

Question 7

How do you check if a property exists in an object?

Accepted Answer

Use `in` operator (`'key' in obj`) or `hasOwnProperty()` to check for a property. `in` includes inherited properties, while `hasOwnProperty()` is stricter. I pick based on whether inheritance matters.

Question 8

How do you reverse a string in JavaScript?

Accepted Answer

You can reverse a string by splitting it into an array, reversing it, and joining it back—like `str.split('').reverse().join('')`. It’s straightforward and readable. For performance, a loop might be better with huge strings, but I usually stick to this.

Question 9

What’s the difference between `null` and `undefined`?

Accepted Answer

`null` is an intentional absence of value, something you set. `undefined` means a variable’s declared but not assigned. I use `null` to reset values and leave `undefined` as the default uninitialized state.

Question 10

What is the purpose of `Object.keys()`?

Accepted Answer

`Object.keys()` returns an array of an object’s enumerable property names. It’s useful for iteration or checking properties. I use it to loop over objects when `for...in` feels clunky.

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