javascript

JavaScript uses prototypal inheritance where objects inherit directly from other objects through a prototype chain. Each object has an internal [[Prototype]] link that forms a chain used for property lookup until null is reached.

Generators are functions that can pause execution and resume later, yielding multiple values over time. They're defined with function* syntax and return an iterator. Use cases include lazy evaluation, infinite sequences, and custom iterables.

A Proxy wraps an object and intercepts fundamental operations (get, set, delete, etc.) through handler traps. They enable metaprogramming patterns like validation, logging, lazy loading, and implementing reactive systems.

JavaScript uses automatic garbage collection with a mark-and-sweep algorithm. Objects are collected when unreachable from roots (global, stack). Memory leaks occur from uncleared references like closures, event listeners, intervals, and DOM references.

The Module pattern encapsulates code using closures to create private state. ES6 modules are the standard with static imports (analyzed at compile time), while CommonJS uses dynamic require() at runtime. ES6 supports tree-shaking and async loading.

CORS (Cross-Origin Resource Sharing) is a browser security mechanism that blocks cross-origin requests unless the server explicitly allows them via HTTP headers like Access-Control-Allow-Origin.

A debounce function delays execution until a pause in calls, using a closure to manage a timer that resets on each invocation. Advanced implementations support leading/trailing edge execution, cancel and flush methods, and a maxWait option to guarantee eventual execution.

A Promise implementation requires managing three states (pending/fulfilled/rejected), storing callbacks via then(), executing them asynchronously when the state transitions, and supporting chaining by returning new Promises from then().

requestIdleCallback schedules low-priority work to run during idle periods when the browser's main thread has no other tasks. Unlike requestAnimationFrame (which runs before every repaint) or setTimeout (which has a minimum delay), it runs only when the browser is truly idle.

WebSockets provide full-duplex, persistent communication between client and server over a single TCP connection. They start as an HTTP upgrade handshake, then switch to a lightweight binary-framed protocol. Use them for real-time features like chat, live notifications, collaborative editing, and live order tracking.

A bind polyfill returns a new function that calls the original with a fixed `this` context and optionally prepended arguments. The implementation must handle partial application, preserve the prototype chain when used with `new`, and forward all arguments correctly.

A JSON.stringify polyfill recursively converts JavaScript values to JSON strings by handling each type differently: strings get quoted, numbers and booleans become literals, arrays and objects are recursively stringified, and special values like undefined, functions, and Symbols are either omitted or converted to null.

Promise.all takes an iterable of promises and returns a single promise that resolves with an array of all results (preserving order) or rejects with the first rejection. Promise.race returns a promise that settles with the first promise to settle, whether fulfilled or rejected.