What is the difference between let and var?

var has function or global scope, can be redeclared and overwritten. It is subject to Hoisting, initialized as undefined.

let has block scope, can be overwritten but not redeclared in the same scope. Also subject to Hoisting, but is in the "temporal dead zone" until initialization.

Comparison table:

Characteristic	var	let
Scope	Function/Global	Block
Redeclaration	Yes	No
Overwrite	Yes	Yes
Hoisting	Yes	Yes
Initialization	undefined	- (temporal dead zone)

Example:

// var
function exampleVar() {
  var x = 10;
  if (true) {
    var x = 20; // Redeclaration of x
    console.log(x); // 20
  }
  console.log(x); // 20
}

// let
function exampleLet() {
  let y = 10;
  if (true) {
    let y = 20; // New variable y in block scope
    console.log(y); // 20
  }
  console.log(y); // 10
}

exampleVar();
exampleLet();