SOURCE

function mulNum(arg1, arg2) {
    var m = 0;
    var s1 = arg1.toString();
    var s2 = arg2.toString();
    try {
        m += s1.split(".")[1].length;
    } catch (e) {}
    try {
        m += s2.split(".")[1].length;
    } catch (e) {}
 
    return Number(s1.replace(".", "")) * Number(s2.replace(".", "")) / Math.pow(10, m);
}
console.log(mulNum(1.5,4.121))