What is the difference between let and var?

You can list out the differences in a tabular format

| var | let |
| -------------------------------------------------------------- | --------------------------------------------- |
| It has been available from the beginning of JavaScript | Introduced as part of ES6 |
| It has function scope | It has block scope |
| Variable declaration will be hoisted, initialized as undefined | Hoisted but not initialized |
| It is possible to re-declare the variable in the same scope | It is not possible to re-declare the variable |

Let's take an example to see the difference,

    function userDetails(username) {
      if (username) {
        console.log(salary); // undefined due to hoisting
        console.log(age); // ReferenceError: Cannot access 'age' before initialization
        let age = 30;
        var salary = 10000;
      }
      console.log(salary); //10000 (accessible due to function scope)
      console.log(age); //error: age is not defined(due to block scope)
    }
    userDetails("John");