Difference between value type and reference type

<script type="text/javascript">

var i = 1;
var j = 2;
var a = [1, 2];

function arr(b) {
  b[0] = 2;
}

function me(x, y) {
 x = x+y;
return x;
}
arr(a);

console.log(i); // 1
console.log(JSON.stringify(a)); // [2,2]
</script>