[Javascript Function] Hitung KPR

hitung_kpr.js

function pmt(rate_per_period, number_of_payments, present_value, future_value, type){
    if(rate_per_period != 0.0){
        // Interest rate exists
        var q = Math.pow(1 + rate_per_period, number_of_payments);
        return -(rate_per_period * (future_value + (q * present_value))) / ((-1 + q) * (1 + rate_per_period * (type)));

    } else if(number_of_payments != 0.0){
        // No interest rate, but number of payments exists
        return -(future_value + present_value) / number_of_payments;
    }

    return 0;
}

function hitung_kpr() {
	var harga = $("#kpr_harga").val(),
		dp = $("#kpr_dp").val(),
		pinjaman = $("#kpr_pinjaman"),
		tahun = $("#kpr_tahun").val(),
		bunga = $("#kpr_bunga").val(),
		result_obj = $("#kpr_result");
	
	if (isNaN(dp)) { alert("isi Persentase Uang muka dengan angka"); return; }
	if (isNaN(bunga)) { alert("isi Bunga dengan angka"); return; }
	
	total_dp = harga * dp / 100;
	total_pinjaman = harga - total_dp;
  
	pinjaman.empty().html(total_pinjaman).number( true, 0 ,',','.');

	total_result = -pmt(bunga/100/12, tahun, total_pinjaman, 0, 0);
  
	result_rupiah = $.number( total_result, 0 ,',','.');
	result_obj.html(result_rupiah);
}