JavaScript interview Questions

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Here you get a free JavaScript Interview Question which helps you to Give Correct Answer of the Question in the Interview. It also helps you for you college exams Preparation.

JavaScript Basics

  1. What is the difference between let, const, and var?
  2. Explain temporal dead zone in JavaScript.
  3. How does JavaScript handle integer precision beyond the Number.MAX_SAFE_INTEGER?
  4. What happens when you use typeof on null? Why?
  5. Explain coercion in JavaScript with an example.
  6. What is the result of [] + [], and why?
  7. Describe the event loop and its relationship to asynchronous JavaScript.
  8. What are the differences between == and ===?
  9. What is the purpose of use strict in JavaScript?
  10. How does JavaScript handle the concept of hoisting?

Functions

  1. How do arrow functions differ from regular functions in terms of this binding?
  2. Can you explain how default parameters work in JavaScript functions?
  3. What is the difference between function declaration and function expression?
  4. Explain what Immediately Invoked Function Expressions (IIFEs) are and why they are used.
  5. What happens when you try to invoke a function with more arguments than parameters?
  6. How does JavaScript implement closures? Provide an example.
  7. Can you explain what currying is in JavaScript?
  8. What is the difference between .call(), .apply(), and .bind()?
  9. How does JavaScript handle recursion, and what are the potential pitfalls?
  10. What is a higher-order function? Provide an example.

Objects and Prototypes

  1. How does the prototype chain work in JavaScript?
  2. What is the purpose of Object.create()?
  3. How can you implement inheritance in JavaScript using prototypes?
  4. Explain the difference between own properties and inherited properties.
  5. What are the differences between Object.seal(), Object.freeze(), and Object.preventExtensions()?
  6. How does hasOwnProperty() differ from the in operator?
  7. What is the difference between a shallow copy and a deep copy? How can they be implemented for objects?
  8. How does the __proto__ property work, and how is it different from the prototype property?
  9. What is the difference between Object.assign() and the spread operator {...}?
  10. Explain how Object.keys(), Object.values(), and Object.entries() work.

Asynchronous JavaScript

  1. What is the difference between synchronous and asynchronous code in JavaScript?
  2. How does JavaScript handle concurrency with the event loop?
  3. Explain how Promises work and how they differ from callbacks.
  4. What are async and await, and how do they improve readability of asynchronous code?
  5. How can you handle multiple Promises simultaneously in JavaScript?
  6. What is a race condition, and how can it be avoided in JavaScript?
  7. Explain the purpose of Promise.race() and Promise.allSettled().
  8. What happens if an error is not caught in a Promise chain?
  9. How does setTimeout() work internally in JavaScript?
  10. What is the role of the microtask queue in JavaScript?

ES6 and Beyond

  1. What are destructuring assignments, and how are they useful?
  2. Explain the purpose of the Symbol type in JavaScript.
  3. How do template literals differ from regular string concatenation?
  4. What are JavaScript modules, and how are they implemented in ES6?
  5. How does Map differ from Object in JavaScript?
  6. Explain the concept of WeakMap and its use cases.
  7. What are the main benefits of using the Set object in JavaScript?
  8. How do rest and spread operators (...) differ in their usage?
  9. What is the purpose of the Reflect API?
  10. How does optional chaining (?.) work, and what problem does it solve?

Error Handling

  1. How does the try...catch block work in JavaScript?
  2. What is the difference between synchronous and asynchronous error handling?
  3. How can custom error classes be created in JavaScript?
  4. What is the purpose of the finally block in error handling?
  5. Explain how throw works in JavaScript.
  6. How does JavaScript handle uncaught exceptions?
  7. What is the purpose of Error.prototype.stack?
  8. How can you create global error handlers in JavaScript?
  9. What is the purpose of the onerror event in JavaScript?
  10. How can errors in Promises be caught using .catch()?

DOM Manipulation

  1. How does document.querySelector() differ from getElementById()?
  2. What is event delegation, and how is it implemented?
  3. How does JavaScript handle bubbling and capturing phases in event handling?
  4. What are the differences between innerHTML, outerHTML, and textContent?
  5. How do you dynamically create and insert elements into the DOM?
  6. What is the purpose of the dataset property on HTML elements?
  7. How can you debounce or throttle events in JavaScript?
  8. What is the difference between addEventListener() and setting onclick directly?
  9. How do stopPropagation() and preventDefault() work in event handling?
  10. What is the shadow DOM, and how does it affect CSS and JavaScript?

Advanced Concepts

  1. What is memoization, and how can it be implemented in JavaScript?
  2. How does Object.defineProperty() work, and what are its use cases?
  3. What are JavaScript decorators, and how do they work?
  4. How do you polyfill a feature in JavaScript?
  5. Explain the concept of function throttling and debouncing.
  6. What is a Proxy in JavaScript, and how is it used?
  7. What is the purpose of a generator function, and how does it work?
  8. Explain the difference between weakMap and map in garbage collection.
  9. What is the difference between an observable and a promise?
  10. How does tail call optimization work in JavaScript?

Performance and Optimization

  1. How do you measure the performance of JavaScript code?
  2. What are the differences between synchronous and asynchronous rendering in JavaScript?
  3. How can you reduce memory leaks in JavaScript applications?
  4. What are Web Workers, and how can they improve performance?
  5. How can you optimize loops in JavaScript?
  6. What is lazy loading, and how can it be implemented in JavaScript?
  7. Explain how the V8 engine optimizes JavaScript execution.
  8. How can tree shaking improve the performance of JavaScript applications?
  9. What is a service worker, and how does it enhance performance?
  10. How can you minimize blocking operations in JavaScript?

Security

  1. How can cross-site scripting (XSS) attacks be prevented in JavaScript applications?
  2. What is content security policy (CSP), and how does it protect JavaScript applications?
  3. How can you prevent cross-site request forgery (CSRF) attacks in JavaScript?
  4. What is the difference between eval() and Function()? Why should eval() be avoided?
  5. How does JavaScript handle CORS (Cross-Origin Resource Sharing)?
  6. What is input sanitization, and why is it important in JavaScript?
  7. Explain how browser same-origin policies work.
  8. What is the purpose of HTTP-only cookies in JavaScript security?
  9. How can you prevent man-in-the-middle attacks in JavaScript applications?
  10. What are the security implications of using localStorage and sessionStorage?

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