JavaScript flashcards, generated for you.

var (function-scoped, hoisted), let (block-scoped, not hoisted to TDZ), const (block-scoped, not hoisted to TDZ, cannot reassign)

== performs type coercion before comparison; === checks both value and type without coercion. Always use === unless you explicitly need coercion.

Declarations are moved to the top of their scope during compilation. var declarations are hoisted and initialized as undefined; let/const are hoisted but not initialized (Temporal Dead Zone).

undefined means a variable has been declared but not assigned a value, or a function has no return statement. null is an intentional assignment representing 'no value' (it's an object type bug in JS).

'this' refers to the object that invoked the current function. In global scope it's the window/global object; in methods it's the object; in arrow functions it's inherited from parent scope; in strict mode it's undefined.

Arrow functions: no own 'this' (inherit from closure), no arguments object, no prototype, cannot use new. Regular functions: have their own 'this' based on how they're called, have arguments object, have prototype.

A function that has access to variables from its lexical parent scope, even after the parent function returns. Created whenever a function is declared; allows data privacy and function factories.

Attaching a single event listener to a parent element to handle events on its children by checking event.target. Benefits: reduced memory usage, handles dynamically added elements, cleaner code.

async/await is syntactic sugar over Promises. async makes a function return a Promise; await pauses execution until the Promise resolves. Makes asynchronous code look/read like synchronous code; try/catch can handle rejections.

Event loop repeatedly checks if call stack is empty; if so, it moves the first callback from the callback queue to the call stack. setTimeout/fetch/events go to callback/microtask queue, not immediately to stack. Microtasks (Promises) run before macrotasks (setTimeout).