JSFiddle - React, Tailwind, and code Playground

HTML

Result :<span id="result"></span>

JavaScript

function addArrayElems(arr) {
    var sum = 0;
    for (var i = 0; i < arr.length; i++) {
        if (typeof arr[i] === "number") 
        {
            sum += parseInt(arr[i]); //parse number and add to sum.
        }
        else if (Object.prototype.toString.call(arr[i]) === '[object Array]')
        {
            sum += addArrayElems(arr[i]);
        }
    }
    return sum;
}
var arr = [1, 2, 3, 4, 5, [6, 7, 8, [9], [10]]];
document.getElementById("result").innerHTML = (addArrayElems(arr));