One-Stop JavaScript Frontend Interview Notes [2026]

If you’re preparing for a frontend interview, this post is your go-to revision guide. We’ve combined quick JavaScript revision notes with real interview coding challenges compiled from top tech companies.
📎 Download JavaScript Frontend Interview Notes (PDF)

🚀 Why These Notes Matter

JavaScript interviews today go beyond basic syntax — they focus on how well you can think, structure, and implement features from scratch.
Our One Stop Frontend Interview Notes PDF (attached below) includes 50+ high-quality coding problems covering every crucial area, such as:

• Event handling (Debounce, Throttle)
• Functional programming (Currying, Pipe)
• Promise utilities (Promise.all, .race, .any)
• Custom implementations of JS features (setTimeout, EventEmitter, Object.assign)
• Deep cloning, flattening, and more

Each problem comes with:

• 🧩 Difficulty level
• 🏢 Companies where it was asked
• 💡 Scenario-based explanation
• 💻 Code implementation + test cases

🧱 Sample Topics from the Notes

1. Debounce Function

Used to delay function execution until a period of inactivity.
Asked in: Meta, Google, IBM
Difficulty: Easy

2. Throttle Function

Executes a function at most once in a given time frame.
Asked in: Google, Tekion
Difficulty: Medium

3. Currying and Currying with Placeholders

Convert a function of N arguments into N functions of one argument each.
Asked in: Amazon, Adobe, Jio
Difficulty: Easy → Medium

4. Promise Utilities

Implement custom versions of:

• Promise.all
• Promise.any
• Promise.allSettled
• Promise.race

Asked in: TikTok, Hotstar, PayPal, Zepto
Difficulty: Medium

5. Polyfills and Custom Implementations

• setTimeout() and setInterval() using requestIdleCallback
• lodash.get() and lodash.set()
• Object.assign, JSON.parse, JSON.stringify
• EventEmitter and custom BrowserHistory

These polyfills test your understanding of JS internals and event loops — the kind of knowledge that sets a strong candidate apart.

🧠 Advanced Case Example: Throttling Promises by Batching

Imagine needing to make 50 concurrent API calls — not efficient!
Instead, you can batch them (e.g., 5 at a time).

function throttlePromises(funcsArr, max) {
  const result = [];
  let nextAPIBatch = 0;

  return new Promise((resolve, reject) => {
    (function fetchAPICalls() {
      const start = nextAPIBatch;
      const end = nextAPIBatch + max;
      const nextAPICalls = funcsArr.slice(start, end);
      const nextPromises = nextAPICalls.map(fn => fn());

      Promise.all(nextPromises)
        .then(data => {
          result.push(...data);
          if (result.length === funcsArr.length) resolve(result);
          else {
            nextAPIBatch = end;
            fetchAPICalls();
          }
        })
        .catch(error => reject(error));
    })();
  });
}

function throttlePromises(funcsArr, max) {
  const result = [];
  let nextAPIBatch = 0;

  return new Promise((resolve, reject) => {
    (function fetchAPICalls() {
      const start = nextAPIBatch;
      const end = nextAPIBatch + max;
      const nextAPICalls = funcsArr.slice(start, end);
      const nextPromises = nextAPICalls.map(fn => fn());

      Promise.all(nextPromises)
        .then(data => {
          result.push(...data);
          if (result.length === funcsArr.length) resolve(result);
          else {
            nextAPIBatch = end;
            fetchAPICalls();
          }
        })
        .catch(error => reject(error));
    })();
  });
}

✅ This implementation efficiently controls concurrency and improves performance.

📘 Download the Full Notes

You can download the complete One Stop Frontend Interview Questions (Preview) PDF here:
📎 Download JavaScript Frontend Interview Notes (PDF)

💬 Includes over 50+ real-world problems from companies like Meta, Google, Adobe, Amazon, and more.

✨ Final Tip for Interviews

• Focus on problem-solving patterns, not just memorizing code.
• Be ready to discuss trade-offs and time complexity.
• Practice writing clean, readable implementations — interviewers value clarity over cleverness.