JavaScript's behavior of moving variable and function declarations to the top of their scope before code execution. var declarations are hoisted and initialized to undefined, while let and const are hoisted but not initialized (temporal dead zone).

The region of code where a variable is accessible. JavaScript has global scope, function scope, and block scope. Block scope was introduced with let and const in ES6.

const declares a block-scoped, read-only reference (the value itself can still be mutated for objects/arrays). let declares a block-scoped, reassignable variable. var declares a function-scoped, hoisted variable. Prefer const by default, let when reassignment is needed, avoid var.