Core JavaScript concepts, ES6+, and browser APIs.
Promises are objects representing the eventual completion or failure of an async operation, providing a cleaner alternative to callbacks.
map for transforming, filter for selecting, reduce for aggregating, find for searching, and forEach for side effects are the essential methods.
Async/await is syntactic sugar over Promises that makes asynchronous code look and behave more like synchronous code.
var is function-scoped and hoisted, let is block-scoped and reassignable, const is block-scoped and can't be reassigned (but objects can be mutated).
A closure is a function that has access to variables from its outer scope, even after the outer function has returned.
Spread operator and Object.assign create shallow copies. For deep copies, use structuredClone or libraries like lodash for nested objects.
Use try/catch for synchronous code and .catch() or try/catch with async/await for promises. Create custom error types for different failure modes.
The 'this' keyword refers to the execution context and its value depends on how a function is called, not where it's defined.
The event loop is a mechanism that allows JavaScript to perform non-blocking operations by offloading operations and using a callback queue.
Use object literals for most cases, classes for complex objects with methods, factory functions for flexible creation, and Object.create for prototypal inheritance.
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