Variables and Scopes
How variable declarations (var, let, const) work and scope rules in JavaScript.
Short explanation
Variables store values and are declared using var, let, or const. var is
function-scoped (or global), while let and const are block-scoped and
prevent certain classes of bugs.
Syntax examples
var a = 1; // function-scoped
let b = 2; // block-scoped
const c = 3; // block-scoped, immutable binding
How JS handles it internally
The JavaScript engine creates bindings in lexical environments. var
declarations are hoisted with an initial value of undefined, while let and
const are hoisted but are in a temporal dead zone until initialized.
Diagram
Related
🔗 Related:
FAQ
Q: When should I use const over let?
A: Prefer const for bindings that won’t be reassigned; it communicates intent
and helps prevent accidental reassignments.