Anyone know how to check if the index of an array item is even

I want to see if the index of the array item is even, if it is then it should carry out a block of code;

var num = 122345643345673;
var convNum = num.toString();
var aftertoString = convNum.split(" ");
function luhnsAlg() {
for (let i = 0; i < aftertoString.length; i++) {
    if (aftertoString[i] == 2) {
        console.log("wow");
    }else{
        console.log("ohh");
    }
  }
}