what is use of var in javascript 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: var javascript

var text = "";
var i;
for (i = 0; i < 5; i++) {
  text += "The number is " + i + "<br>";
}