JSFiddle - React, Tailwind, and code Playground

JavaScript

function AdditivePersistence(num) {
    var loop = 0;
    var numbers = num.toString();
    while (numbers.length > 1) {
        var res = 0;
        res += numbers.split('').reduce(function (a, b) {
            return Number(a) + Number(b)
        });
        numbers = res.toString();
        loop++;
    }

    return loop;
}
console.log(AdditivePersistence(2718));