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What is JavaScript? Explain its role in web development and key characteristics.
Explain the differences between var, let, and const in JavaScript. How do they affect variable scope and reassignment?
What are the primitive data types in JavaScript? Explain the difference between null and undefined.
What are the different ways to define functions in JavaScript? Compare function declarations, function expressions, and arrow functions.
Explain truthy and falsy values in JavaScript. How does type coercion work with equality operators (== vs ===)?
What is hoisting in JavaScript? How does it work with var, let/const, and function declarations?
What are common array methods in JavaScript? Explain map, filter, and reduce with examples.
How do you create and manipulate objects in JavaScript? Explain object literal syntax, property access, and dynamic properties.
How do you select and manipulate DOM elements using JavaScript? Explain methods like getElementById, querySelector, and modifying content/attributes.
How does event handling work in JavaScript? Explain addEventListener, event object, and event propagation basics (bubbling and capturing).
What are Promises in JavaScript? Explain states (pending, fulfilled, rejected) and how to chain them using .then() and .catch().
How does async/await work in JavaScript? Explain how to handle errors with try/catch.
How do you make HTTP requests using the Fetch API? Explain response handling, JSON parsing, and error handling.
How does error handling work in JavaScript using try, catch, finally, and throw? Give an example with asynchronous code.
What are template literals in JavaScript? Explain string interpolation, multi-line strings, and tagged templates.
What is destructuring assignment in JavaScript? Provide examples for arrays and objects.
Explain the spread and rest operators (...) in JavaScript. How are they used in arrays, objects, and function parameters?
How does localStorage and sessionStorage work in web browsers? Explain use cases and limitations.
Compare different looping mechanisms in JavaScript: for, for...of, for...in, forEach, and while loops.
What is the 'this' keyword in JavaScript? How does its value differ in global scope, function context, and arrow functions?
How do you parse and stringify JSON in JavaScript? Explain JSON.parse() and JSON.stringify() with examples.
Explain explicit and implicit type conversion in JavaScript. Provide examples of converting to string, number, and boolean.
What is a closure in JavaScript? Provide a simple example and explain lexical scoping.
How do setTimeout and setInterval work in JavaScript? Explain their asynchronous nature and how to clear them.
What are closures in JavaScript? Explain how they work with practical examples and discuss memory implications.
Explain the prototype chain in JavaScript. How does prototypal inheritance differ from classical inheritance?
What are call, apply, and bind? How do they differ and when would you use each?
What is event delegation? How does it work and why is it useful? Provide an example.
Explain debounce and throttle. Provide implementation examples and use cases.
Explain the JavaScript execution context. What is the event loop and how do microtasks and macrotasks differ?
What are common memory leaks in JavaScript applications? How to detect and fix them?
What is the difference between deep copy and shallow copy? How to implement each in JavaScript?
Compare ES modules (import/export) with CommonJS (require/module.exports). What are the key differences in loading, syntax, and usage?
What are WeakMap and WeakSet? How do they differ from Map and Set, and when should you use them?
What are Symbols in JavaScript? How are they used as unique property keys and well-known symbols?
What are iterators and generators in JavaScript? Provide examples and explain their relationship with the iteration protocol.
How does AbortController work? Demonstrate canceling fetch requests and other async operations.
What are common JavaScript performance optimization techniques? Explain reflow, repaint, and how to minimize layout thrashing.
How does the MutationObserver API work? Compare it with deprecated DOM events and provide a use case.
What is IntersectionObserver? How does it improve scroll performance compared to scroll event listeners?
What is the Node.js event loop? Explain its phases and how it differs from the browser event loop.
Explain Node.js Streams. What are the types of streams (Readable, Writable, Duplex, Transform) and how do you handle backpressure?
Compare IndexedDB, localStorage, and sessionStorage. When would you use IndexedDB over other storage mechanisms?
What is Promise.all, Promise.allSettled, Promise.race, and Promise.any? Provide examples and use cases.
How does JIT compilation work in JavaScript engines (e.g., V8)? Explain the role of Ignition, Sparkplug, and TurboFan.
Explain garbage collection in JavaScript (mark-and-sweep, generational collection). How do memory leaks occur and how to use WeakRef and FinalizationRegistry?
How does the event loop interact with the microtask and macrotask queues in different environments (browser vs Node.js)? Explain event loop starvation.
What are Proxies and Reflect in JavaScript? Explain advanced use cases like validation, logging, and reactive systems.
How would you implement a custom Promise from scratch? Explain the core components (resolve, reject, then, chaining).
What are polyfills and transpilers? Explain how Babel works (AST, transforms, and polyfill injection).
Explain module bundling internals (Webpack, Vite). How do they resolve dependencies, handle code splitting, and optimize production builds?
How does the libuv thread pool work in Node.js? Explain how it handles async I/O and which operations use the pool vs native async.
How does the Node.js cluster module work? Explain multi-process architecture, load balancing, and differences from worker threads.
Explain backpressure in Node.js streams. How does pipe() handle it and how to implement custom backpressure handling?
What are common JavaScript security vulnerabilities (XSS, CSRF, prototype pollution)? How to prevent them in production apps?
How do you architect a production-grade Node.js application? Discuss error handling, logging, monitoring, and graceful shutdown.
Explain advanced JavaScript design patterns: Module, Singleton, Factory, Observer, and their modern ES6+ implementations.
What are critical rendering path optimizations? How do you reduce layout shifts and improve Core Web Vitals (LCP, FID, CLS)?
How do you implement a reactive system using Proxies (similar to Vue 3)? Explain dependency tracking and effect scheduling.
What are the Temporal API and other modern JavaScript proposals (Records/Tuples, Decorators, Pipeline operator)? Explain how they improve the language.
Explain compositing layers in the browser and how to use will-change, transform, and opacity for GPU acceleration.
Explain how JavaScript engines optimize array operations: packed vs holey arrays, SMI vs double elements, and array methods performance.