Javascript Function to calculate Periodic Payments(PMT)

// Function to calculate Periodic Payments.

function pmt(rate, per, nper, pv, fv) {

    fv = parseFloat(fv);

    nper = parseFloat(nper);

    pv = parseFloat(pv);

    per = parseFloat(per);

    if ((per == 0) || (nper == 0)) {

        alert("Why do you want to test me with zeros?");

        return (0);

    }

    rate = eval((rate) / (per * 100));

    if (rate == 0) // Interest rate is 0
    {

        pmt_value = -(fv + pv) / nper;

    }

    else {

        x = Math.pow(1 + rate, nper);

        pmt_value = -((rate * (fv + x * pv)) / (-1 + x));

    }

    pmt_value = conv_number(pmt_value, 2);

    return (pmt_value);

}

//end Of PMT