US_phone_format

const test_array = [2,1,2,5,5,5,0,1,2,3];

//using for loop
function format_phone_number(array)
{
    let result = "";
    for (i in array)
    {
        if (i == 0)
        {
            result += "(";
        }
        if (i == 6)
        {
            result += "-";
        }
        result += array[i];
        if (i == 2)
        {
            result += ") "
        }

    }
    console.log(result);
    return result;
}


//using slice and join
function format_phone_number(array)
{
    first = array.slice(0,3);
    second = array.slice(3,6);
    third = array.slice(6);
    result = "(" + first.join("") + ") " + second.join("") + "-" + third.join("");
    return result;
}