<script> var x="Tech Altum"; // value of x is "Tech Altum"; var y='Tech Altum'; // value of y is also "Tech Altum"; var z=9; // value of z is 9 numeric. var a=2, b=3, c=5; // multiple variables in single line var u; // u is undefined </script>
let and const were introduced in ECMA 6.
<script> let x="user"; // x can't be changed const pi=Math.PI; // pi is a constant </script>
Although it is not compulsory to start variables with var keyword, but still we prefer var. let and const are supported in IE 11 and above, edge, firefox 36 and above, chrome 21 and above ans safari 5.1 and above.