Describe the difference between the var and let keywords in JavaScript.

In JavaScript, var and let both declare variables, but they differ in scope, hoisting, and re‑declaration rules. var is function‑scoped or globally scoped if declared outside a function. It is hoisted to the top of its scope and initialized with undefined, allowing the variable to be referenced before its declaration (though the value will be undefined). var also permits redeclaration within the same scope, which can lead to accidental overwrites.

let, introduced in ES6, is block‑scoped, meaning it is only accessible within the nearest {} block, loop, or conditional. It is also hoisted but not initialized, creating a "temporal dead zone" (TDZ) where accessing the variable before its declaration throws a ReferenceError. let does not allow redeclaration in the same scope, helping prevent accidental variable shadowing.

Because of these differences, let is preferred for most modern code: it provides clearer scoping, avoids accidental redeclarations, and reduces bugs related to hoisting. var is still used in legacy code or when function‑scoped variables are explicitly needed.