JSFiddle - React, Tailwind, and code Playground

JavaScript

var nCtrr = 0, nSum = 0, nAvg = 0;
var arNum = [1, 2, 3, 4, 5];
for ( nCtr in arNum ) {

    nSum += arNum[ nCtr ];
    nCtr += 1;

}
nAvg = nSum/arNum.length;
alert( nAvg );