فرق بین let و var در javascript چیست؟

“var” has no block scope
Variables, declared with var, are either function-wide or global. They are visible through blocks.

if (true) {
  var test = true; // use "var"
}
alert(test); // true, the variable lives after if

if (true) {
  let test = true; // use "let"
}
alert(test); // Error: test is not defined