Windows7 の電卓についていたアレ (住宅ローンの計算)
Windows7 の電卓についていた住宅ローンの計算が Windows10 で見当たらないので、HTML と JavaScript で再現してみました。
下記のソースをUTF-8で保存後、Microsoft Edge 等のブラウザで読み込んでご利用ください。
計算精度は素の JavaScript のままですので、小数点以下の細かいところは本家の電卓と一致していません。
calc_loan.html
<!DOCTYPE html>
<html lang="ja">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<meta charset="UTF-8" />
<title>Windows7 の電卓についていたアレ (住宅ローンの計算)</title>
<script type="text/javascript">
'use strict';
(function(window, document) {
//==================================================================================================
let $ = e => document.getElementById(e);
//==================================================================================================
class MyLoan {
constructor() {
this.Price = 0; //購入価格
this.Deposit = 0; //頭金
this.Years = 0; //期間 (年数)
this.YearRate = 0; //利率 (%)
this.PerMonthPayment = 0; //毎月の支払い
}
//購入価格
Calc_Price() {
const manth_rate = this.YearRate / 100 / 12; //月あたりの利率
const payment_num = this.Years * 12; //支払い回数
this.Price = this.Deposit +
(this.PerMonthPayment * ((1 + manth_rate) ** payment_num - 1)) / (manth_rate * ((1 + manth_rate) ** payment_num));
return this.Price;
}
//頭金
Calc_Deposit() {
const manth_rate = this.YearRate / 100 / 12;
const payment_num = this.Years * 12;
this.Deposit = this.Price -
(this.PerMonthPayment * ((1 + manth_rate) ** payment_num - 1)) / (manth_rate * ((1 + manth_rate) ** payment_num));
return this.Deposit;
}
//期間 (年数)
Calc_Years() {
const manth_rate = this.YearRate / 100 / 12;
//rate = (1 + manth_rate) ** payment_num;
let rate = this.PerMonthPayment / (this.PerMonthPayment - (this.Price - this.Deposit) * manth_rate);
if (rate <= 0) { return "error: 毎月の支払い額が不足しています"; }
let payment_num = Math.log(rate) / Math.log(1 + manth_rate);
this.Years = payment_num / 12;
return this.Years;
}
//毎月の支払い額
Calc_PerMonthPayment() {
const manth_rate = this.YearRate / 100 / 12;
const payment_num = this.Years * 12;
this.PerMonthPayment = (this.Price - this.Deposit) * manth_rate * ((1 + manth_rate) ** payment_num)
/ ((1 + manth_rate) ** payment_num - 1);
return this.PerMonthPayment;
}
}
//==================================================================================================
window.onload = function() {
$("selType").onchange = () => {
const calctype = $("selType").options[$("selType").selectedIndex].value;
$("txtResult").value = $("txt" + calctype).value;
$("tr" + $("hidCurrentType").value).style.visibility = "visible";
$("hidCurrentType").value = calctype;
$("tr" + calctype).style.visibility ="collapse";
}
$("btnCalc").onclick = () => {
const objLoan = new MyLoan();
objLoan.Price = $("txtPrice").value - 0; //購入価格
objLoan.Deposit = $("txtDeposit").value - 0; //頭金
objLoan.Years = $("txtYears").value - 0; //期間 (年数)
objLoan.YearRate = $("txtYearRate").value - 0; //利率 (%)
objLoan.PerMonthPayment = $("txtPerMonthPayment").value - 0; //毎月の支払い
const calctype = $("selType").options[$("selType").selectedIndex].value;
switch (calctype) {
case "Years":
$("txtResult").value = objLoan.Calc_Years();
$("txtYears").value = $("txtResult").value;
break;
case "Price":
$("txtResult").value = objLoan.Calc_Price();
$("txtPrice").value = $("txtResult").value;
break;
case "Deposit":
$("txtResult").value = objLoan.Calc_Deposit();
$("txtDeposit").value = $("txtResult").value;
break;
case "PerMonthPayment":
$("txtResult").value = objLoan.Calc_PerMonthPayment();
$("txtPerMonthPayment").value = $("txtResult").value;
break;
}
}
}
//==================================================================================================
})(window, document);
</script>
<style type="text/css">
h1 { font-size:x-large;margin-bottom:0; }
input[type="button"] { margin-left:0px;width:100px; }
#tbLoan { border: solid 1px #222222; }
#tbLoan input[type="number"] { margin-left:0px;margin-right:0px;width:96%; }
#tbLoan input[type="text"] { margin-left:0px;margin-right:0px;width:96%; }
#trYears { visibility:collapse; }
input[type="number"]:invalid { border:solid 3px red; outline:0; }
</style>
</head>
<body style1="padding-top:0px;margin-top:0px;">
<h1>Windows7 の電卓についていたアレ (ワークシート > 住宅ローン)</h1>
※計算精度は生JavaScriptのままです。<br />
<br />
<table id="tbLoan" style="width:450px;">
<tr><td colspan="2">計算する値を選択してください</td></tr>
<tr>
<td colspan="2">
<select id="selType" style="width:100%;">
<option id="optYears" value="Years">期間 (年数)</option>
<option id="optPrice" value="Price">購入価格</option>
<option id="optDeposit" value="Deposit">頭金</option>
<option id="optPerMonthPayment" value="PerMonthPayment">毎月の支払い額</option>
</select>
</td>
</tr>
<tr id="trPrice"><td>購入価格</td><td><input type="number" id="txtPrice" min="0" value="" /></td></tr>
<tr id="trDeposit"><td>頭金</td><td><input type="number" id="txtDeposit" min="0" value="" /></td></tr>
<tr id="trYears"><td>期間 (年数)</td><td><input type="number" id="txtYears" min="0" value="" /></td></tr>
<tr id="trYearRate"><td>利子率 (％)</td><td><input type="number" id="txtYearRate" step="0.0001" value="" /></td></tr>
<tr id="trPerMonthPayment"><td>毎月の支払い額</td><td><input type="number" id="txtPerMonthPayment" min="0" value="" /></td></tr>
<tr><td> </td><td></td></tr>
<tr><td><input type="button" id="btnCalc" value="計算" /></td><td><input type="text" id="txtResult" value="" readonly="readonly" /></td></tr>
</table>
<input type="hidden" id="hidCurrentType" value="Years" />
</body>
</html>