Array.isArray() — JS Technical Interview Questions & Answers

Checks whether a value is an array.

Array.isArray()

  • Array.isArray() is a JS topic. In plain words you use it for fail students only in a marks list. Don’t start with a slogan — start with that picture.
  • Smallest example: filter(m => m < 40). Type it, run it, and say what you see. If you can do that from memory, you know Array.isArray().
  • From the example next to this theory: Checks whether a value is an array.
  • Trap: mutating while filtering. Fix that before you talk about advanced JS.
  • Viva: what is Array.isArray()? Then show filter(m => m < 40). Then name the trap.

Technical Interview Tip: What is Array.isArray()? Show this: filter(m => m < 40). Trap: mutating while filtering.

Code Examples for Array.isArray()

Array.isArray() — working example

const nums = [1, 2, 3, 4, 5];
const evens = nums.filter((n) => n % 2 === 0);
const doubled = evens.map((n) => n * 2);
const sum = doubled.reduce((a, b) => a + b, 0);
console.log(evens, doubled, sum);
console.log(nums.includes(3), nums.find((n) => n > 3));

Array.isArray() — common array methods return new values (filter/map/reduce) or search without mutating.

How to Explain Array.isArray() to an Interviewer

What is Array.isArray()?

Used for fail students only a marks list Not just the heading

Give one small example of Array.isArray().

filter(m => m < 40) Checks whether a value is an array

What mistake do beginners make with Array.isArray()?

mutating while filtering Show the fix

Where do you use Array.isArray()?

a marks list fail students only