SOURCE

function accAdd(arg1, arg2) {
    let r1, r2, max, m, num;
    try { r1 = arg1.toString().split(".")[1].length } catch (e) { r1 = 0 };
    try { r2 = arg2.toString().split(".")[1].length } catch (e) { r2 = 0 };
    max = Math.max(r1, r2);
    m = Math.pow(10, max);
    num = (arg1 * m + arg2 * m) / m;
    if (num.toString().indexOf('.') > 0) {
        return num.toFixed(max);
    } else {
        return num;
    }
}

let a = [0.6211, 0.6211, 0.6211,0.6211, 0.6211, 0.6211,0.6211, 0.6211, 0.6211]
let c = 0;
for (let s of a) {
    c = accAdd(c,s)
}

console.log(c)