If you’re preparing for JavaScript Interview role or aiming to strengthen your JavaScript fundamentals, real-world interview scenarios are the best way to understand what to expect. This blog shares a complete JavaScript interview walkthrough, from technical coding tasks to deep-dive theory discussions. The candidate’s performance, clarity, and quick problem-solving skills reflect the level of preparation expected for today’s developer roles.
The Interview Begins: JavaScript Interview
The session started with brief introductions. The interviewer, a former full-stack developer from a London-based fintech company, explained his background working with no-code platforms and global projects.
The candidate, Akash, introduced himself as an MCA graduate with hands-on experience in more than 17 live projects. His journey included WordPress, Shopify, and advanced work in JavaScript and ReactJS. He highlighted being selected for a prestigious entrepreneurial program — a government initiative that picks only 500 out of over 50,000 applicants. His consistent practice streak of 150+ days on LeetCode added further credibility to his technical discipline.
Problem-Solving with JavaScript: Working with JSON Data
The first coding challenge involved working with a JSON object. The task was to calculate the sum of student marks greater than 50 after applying grace marks.
Akash tackled this efficiently by:
- Parsing the JSON structure
- Iterating through the array
- Filtering students with marks above the threshold
- Summing the valid entries
After a quick syntax correction (replacing parenthesis with curly braces), the code worked perfectly. He also shared the time and space complexity using Big O notation, a vital component of coding interviews.
JavaScript Project Task: Implementing a To-Do App
Next, the interviewer shifted gears and asked for a small implementation task — building a to-do list application.
Requirements: JavaScript Interview
- An input field
- A submit button
- Displaying the input as a task when the button is clicked
Akash explained the basic logic:
- Capture the input using JavaScript event listeners
- Append the text as a new element in the DOM
- Ensure updates render instantly on the page
Although CSS was not a priority, his focus on functional behavior demonstrated practical frontend skills.
DOM Manipulation in JavaScript
The interview briefly touched on DOM manipulation. Akash explained how developers can modify and interact with web page elements using: JavaScript Interview
getElementByIdgetElementsByClassNamequerySelectorgetElementsByTagName
These methods help change content, structure, and behavior dynamically, enabling modern interactive UIs.
Theoretical Concepts: HTML, CSS, JavaScript
A rapid round of core concepts followed.
📦 What is the Box Model?
Akash accurately defined the CSS Box Model — a foundational UI layout concept:
- Content: The inner content like text or images
- Padding: Space around the content inside the border
- Border: Wraps the padding and content
- Margin: Space outside the border, separating elements
⬇️ How to Create a Dropdown in HTML?
Though slightly hesitant at first, he correctly recalled using the <select> tag and nested <option> elements to build dropdowns in HTML.
🚀 What is Hoisting?: JavaScript Interview
He explained hoisting in JavaScript as the mechanism where variable and function declarations are moved to the top of their scope during compilation. Only declarations are hoisted — not initializations. This helps explain common interview pitfalls like ReferenceError or undefined.
🌊 What is Event Propagation?
Event propagation was described as how events flow through the DOM tree:
- Capturing Phase (from top to target)
- Target Phase
- Bubbling Phase (from target back up)
He also mentioned the use of addEventListener with capture options for controlling this flow.
⏳ Understanding Promises in JavaScript: JavaScript Interview
Promises were explained clearly as objects representing eventual completion (or failure) of asynchronous tasks. Akash described:
- Pending: Initial state, waiting for result
- Fulfilled: Task completed successfully
- Rejected: Task failed, error thrown
He also touched on the practical use of Promises with APIs, which is common in front-end development.
Final Impressions and Feedback
As the session came to a close, the interviewer acknowledged Akash’s clarity, practical coding confidence, and eagerness to learn. No doubt, his preparation stood out.
He wrapped up the session with a friendly note and encouragement, highlighting that with this level of dedication and discipline, cracking any front-end or JavaScript-focused role would be absolutely achievable.
Key Takeaways for JavaScript Interview Prep
If you’re preparing for similar interviews, here’s what to focus on:
✅ Practice JSON Parsing and basic logic problems
✅ Work on mini projects like to-do apps, calculators, or dynamic forms
✅ Master DOM methods — they’re asked frequently
✅ Revise core concepts like hoisting, event bubbling, promises, and box model
✅ Speak out loud while coding — it shows confidence and clarity
Final Thoughts
This mock interview session is a great blueprint for anyone aiming to build a strong career in frontend or JavaScript development. Whether you’re applying for startups, MNCs, or product-based companies, real-time application of concepts matters more than just theory.
So, keep practicing, stay curious, and get ready to ace your next JavaScript interview.