Technologies Coding Problems Bookmarks Learning Paths

Technologies Coding Problems Bookmarks Learning Paths

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What is an array in JavaScript? | Array Operations | javascript Interview Questions | NextRound.in

Questions

14 of 14

1Write your own function to flatten a nested array.

2Array Cheatsheet.

3Flatten a deeply nested array of numbers and return most frequent number with its count

4How to sort array of objects?

5Find maximum and minimum number of an array.

6How to sort an array?

7What is the purpose of the `Array.prototype.filter()` method?

8What is the purpose of the `forEach()` function for arrays?

9What is the purpose of the `reduce()` function for arrays?

10What is the purpose of the `map()` function for arrays?

11Explain the difference between the `for...of` and `for...in` loops.

12What is the purpose of the `Array.isArray()` method?

13How do you loop through an array?

14What is an array in JavaScript?

javascript

Event Loop and Runtime

Concurrency and Threading

Bytecode and Parsing

Execution Context

String Operations

Array Operations

Call Apply Bind

Iterator and Generator

Garbage Collector

Functional Programming

Higher Order Functions

14 / 14

What is an array in JavaScript?

Difficulty: 2/10

indexing, mutation, performance

1
An array is a data structure that holds a list of elements.
2
Each element is identified by its index, starting from 0. You can create an array using square brackets []

javascript

Scenario Questions

0-2 years experience

1You receive an API response with a list of user IDs and need to display the third ID; how would you store and access it using a JavaScript array, and what happens if fewer than three IDs are returned?
2Given `let nums = [1, 2, 3];`, what does `nums[5]` evaluate to and why?
3How would you add a new element to the end of an array without mutating the original array?

Follow-up Questions

What is the time complexity of accessing an element by index?
How do sparse arrays differ from dense ones in memory usage?
When would you prefer `push` over `unshift` for adding items?

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2-5 years experience

1A function doubles each number in an input array using a for‑loop but sometimes throws `undefined is not a function`. Walk me through how you'd debug the issue.
2When merging two sorted arrays you notice duplicate entries in the result. Explain a possible cause related to array methods and how you'd fix it.
3Your React component receives a prop that should be an array of objects, but occasionally gets `null`. How would you safely iterate over it without causing a runtime error?

5-8 years experience

1Our service processes JSON payloads containing arrays up to 10 million items. What memory or performance concerns arise with native arrays, and what alternatives or patterns would you consider?
2We need a sliding window over a large array of events to compute a moving average in real time. Describe an efficient algorithm and discuss the trade‑offs of mutating the original array versus using a circular buffer.
3A legacy codebase frequently uses `Array.prototype.splice` to remove items, causing UI jank. How would you refactor the code to improve responsiveness while preserving behavior?

8+ years experience

1Our public API returns large collections of data. We're debating between returning a plain JavaScript array versus a paginated cursor/stream. What architectural factors influence your recommendation?
2Multiple teams share a utility library for array manipulation across micro‑frontends. How would you design a versioned, type‑safe helper module to avoid breaking changes?
3We plan to migrate a performance‑critical component from JavaScript arrays to WebAssembly typed arrays. Outline the migration steps and the risks you would mitigate.