should I use var in js code example

Example 1: js var

var a;
console.log(a);                // scrive in console "undefined" o "" a seconda del browser usato.
console.log('still going...'); // scrive in console "still going...".

Example 2: variables in js

Variables can have anything, you define them as equal to something
    
    eg:   var x = 22
    var statement = 'hello!'
    var isAbool = true 
    
    there are three types of variables:
1. var 
2. let
3. const 

var is a normal variable
let is a variable whose value can be changed eg: let h = 12, h = 10(we changed the value, if you run this, there will be no error)
const is a variable whose value cannot be changed, if you change the value of a const, you will have errors in you code