JavaScript Interview Questions - Coding Interview 2026

Highlight words longer than eight characters in a paragraph by using javascript and dom methods, querySelector, splitting the text, mapping, and wrapping long words with a yellow background.

Create a link by using document.createElement, set its href to ipsum.com, assign link text from lorem ipsum, and append the anchor to the end of the document body.

Practice turning a paragraph into separate lines by sentence using a robust regular expression, handling single and multiple dots, escaping dots, and using global and multiline flags.

Demonstrates event delegation by replacing thousands of item listeners with a single listener on the app container, checking event.target's class to handle item clicks efficiently.

Learn how to implement an XMLHttpRequest to fetch data from GitHub, handle open, send, status checks, and success or error callbacks with console logs.

Learn how the fetch API uses promises, then and catch for handling results, convert responses to JSON, and compare modern, readable code with older approaches.

Learn how callbacks enable asynchronous JavaScript, using setTimeout to simulate data fetch, and see how a generic callback lets a synchronous function defer work and handle results.

Execute a parallel async function that runs an array of asynchronous functions, waits for all to complete, and returns the results in order via a single callback.

Learn to map users with promises by fetching users and statuses in parallel using Promise.all, then merge data into id, name, and isActive via map.

Rewrite mapping data in async await to read asynchronous operations as synchronous code using get mapped users and get user statuses. Implement try/catch for error handling and resolve promises.

Master correct vocabulary in JavaScript by using terms like function, method, class, and instance. Describe your program accurately to avoid misunderstandings and project confidence in interviews.

Design a recursive request manager that fetches data from a given url, retries with increasing delay and timeout on failure for a set number of attempts, using promises.

Learn to implement shallow comparison in JavaScript to compare primitives, arrays, and objects by value rather than reference, and know when deep comparison is needed for nested data.

Learn to convert a shallow compare into a deep compare by recursively checking nested arrays and objects. See how primitives, arrays, and objects are handled, with performance notes.

Create a memorization function in JavaScript that uses a closure and cache to add 10 to a value, returning cached results on repeat calls.

Explore how to implement Fibonacci in JavaScript using recursion, understand the Fibonacci sequence, and learn interview wisdom about when to memorize formulas.

Learn how to implement a palindrome function in JavaScript by reversing a string with split, reverse, and join, and comparing it to the original to identify palindromes.

Implement a JavaScript isAnagram function that checks length, lowercases both strings, sorts their letters, and compares results with examples like listen and silent.

Count vowels in a string with a JavaScript function, exploring both for-loop and reduce approaches, using a vowel set, lowercase conversion, and character iteration for a clean, functional solution.

Convert a 12-hour time input to 24-hour format in JavaScript by lowercasing, splitting hours and minutes, applying am/pm rules (including 12 a.m. and 12 p.m.), and padding zeros with padStart.

Map data from the back end to the front end by aligning the location key with the bulk config, producing a one-to-one structure for five objects.

Learn to build a generic JavaScript function to replace URL parameters using a replacements array, iterating with reduce to update an accumulator without mutating the original URL.

Learn to transform backend validation errors into a frontend friendly format by mapping object entries, concatenating field messages, and producing a human readable 'field: message' list.

Transform a flat list into a nested list by identifying root elements and recursively attaching children by id, using non-mutating object copies to form each node’s children array.

Master JavaScript interview questions through practical homework, completing 59 coding interview problems and sharpening problem-solving skills, preparation strategies, and mindset for interview success.