JavaScript Developer interview questions

Best practices involve minimizing direct DOM event bindings, using event delegation for dynamically generated elements, properly managing event propagation using stopPropagation and preventDefault only when necessary, and structuring event listeners to avoid memory leaks in complex component hierarchies.

Common challenges include callback hell, error handling, and race conditions. These are addressed by adopting Promises or async/await syntax for readability, using try/catch blocks for error management, and employing utilities like Promise.all or race to handle concurrency.

Closures allow functions to retain access to their lexical scope, enabling private state and encapsulation of logic. This supports modular code by restricting access to variables and functions that should not be exposed globally, thus improving maintainability and preventing naming conflicts.

Considerations include detaching event listeners before removing DOM nodes, avoiding circular references, using weak references where possible, and leveraging frameworks' lifecycle hooks to ensure cleanup. Regular code audits and tools like browser dev tools help identify lingering listeners.

Approaches include using async/await to write sequential-like code, chaining Promises for ordered execution, leveraging Promise.all for parallel tasks, and employing async control flow libraries for more complex scenarios like waterfalls and series execution.

Hoisting moves declarations to the top of their scope, which may lead to unexpected undefined variables or overwrite function declarations. Understanding hoisting helps senior developers avoid scoping bugs, especially when mixing var, let, and const declarations within closures or callback contexts.

Strategies include refactoring nested callbacks into named functions, using Promises or async/await to flatten the control flow, modularizing reusable logic, and applying error handling patterns such as central catch handlers to keep the codebase manageable.

Event throttling and debouncing are implemented using timer functions to limit how frequently a handler executes—throttling calls the handler at most once per specified interval, while debouncing delays execution until repeated events cease. These techniques improve performance for resize, scroll, keyboard, or mouse events.

Closures enable advanced asynchronous optimizations such as memoization, deferred execution, and maintaining private state across asynchronous operations. They also facilitate the creation of higher-order functions and custom control flow utilities for handling async processes.

Factors include understanding ES6 module scope isolation, distinguishing between block (let/const) and function (var) scoping, preventing lexical scope pollution, and leveraging module bundlers to maintain clear and predictable variable scope boundaries in large applications.