javascript之小应用-贷款计算器 -

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javascript之小应用-贷款计算器

博客分类：

javaScript

javascript html5

犀牛书上的
基于JavaScript实现的贷款计算器：

<!DOCTYPE html>
<html>
<head>
    <title>JavaScript Loan Calculator</title>
    <style>
        .output{font-weight:bold;}
        #payment{text-decoration:underline;}
        #graph{border:solid black 1px;}
        th,td{vertical-align:center;}
    </style>

</head>
<body>
    <table>
        <tr>
            <th>Enter Loan Data:</th>
            <td></td>
            <th>Loan Balance,Cumulative Equity,and Interest Payments</th>
        </tr>
        <tr>
            <td>Amount of the loan($):</td>
            <td><input id='amount' onchange='calculate();'></td>
            <td rowspan=8>
                <canvas id='graph' width='470' height='250'></canvas>
            </td>
        </tr>
         <tr>
            <td>Annual interest(%):</td>
            <td><input id='apr' onchange='calculate();'></td>           
        </tr>
         <tr>
            <td>Repayment period(years):</td>
            <td><input id='years' onchange='calculate();'></td>           
        </tr>
         <tr>
            <td>Zipcode(to find lenders):</td>
            <td><input id='zipcode' onchange='calculate();'></td>           
        </tr>
         <tr>
            <td>Approximate Payments:</td>
            <td><button onclick='calculate();'>Calculate</button></td>           
        </tr>
         <tr>
            <td>Monthly Payments:</td>
            <td>$<span class='output' id='payment'></span></td>           
        </tr>
         <tr>
            <td>Total Payments:</td>
            <td>$<span class='output' id='total'></span></td>           
        </tr>
         <tr>
            <td>Total Interest:</td>
            <td>$<span class='output' id='totalinterest'></span></td>           
        </tr>
         <tr>
            <th>Sponsors:</th>
            <td colspan=2>
                Apply for your loan width one of these fine lenders:
                <div id='lenders'><div>
            </td>              
        </tr>
    </table>
    <script type="text/javascript">
        "use strict";
        function $(id){
            return document.getElementById(id);
        }
        
        function calculate (){
            var amount = $('amount');
            var apr = $('apr');
            var years = $('years');
            var zipcode = $('zipcode');
            var payment = $('payment');
            var total = $('total');
            var totalinterest = $('totalinterest');
           
            var principal = parseFloat(amount.value);
            var interest = parseFloat(apr.value)/100/12;
            var payments = parseFloat(years.value)*12;
          
            var x = Math.pow(1+interest ,payments);// power method.
            var monthly = (principal * x * interest)/(x-1);
            
            if(isFinite(monthly)){
                payment.innerHTML = monthly.toFixed(2);
                total.innerHTML = (monthly*payments).toFixed(2);
                totalinterest.innerHTML = ((monthly*payments)-principal).toFixed(2);                
                save(amount.value,apr.value,years.value,zipcode.value);            
                try{
                    getLenders(amount.value,apr.value,years.value,zipcode.value);
                }catch(e){}                
                chart(principal,interest,monthly,payments); 
            }else{                
                payment.innerHTML = "";
                total.innerHTML = "";
                totalinterest.innerHTML = "";
                chart();
            }
        }
        
        function save(amount,apr,years,zipcode){
            if(window.localStorage){
                localStorage.loan_amount = amount;
                localStorage.loan_apr = apr;
                localStorage.loan_years = years;
                localStorage.loan_zipcode = zipcode;
            }
        }
        
        window.onload = function(){
            if(window.localStorage&&localStorage.loan_amount){
                $('amount').value = localStorage.loan_amount;
                $('apr').value = localStorage.loan_apr;
                $('years').value = localStorage.loan_years;
                $('zipcode').value = localStorage.loan_zipcode;
            }
        }
        
        function getLenders(amount,apr,years,zipcode){
            if(!window.XMLHttpRequest)return ;            
            var ad = $('lenders');
            if(!ad)return;
            
            var url = 'getLenders.php' + 
                      '?amt='+ encodeURIComponent(amount)+
                      '&apr='+ encodeURIComponent(apr)+
                      '&yrs='+ encodeURIComponent(years)+
                      '&zip='+ encodeURIComponent(zipcode);
            
            var req = new XMLHttpRequest();
            req.open('GET',url);
            req.send(null);
            
            req.onreadystatechange = function(){
                if(req.readyState==4 && req.status == 200){
                    var response = req.responseText;
                    var lenders = JSON.parse(response);                    
                    var list = '';
                    for(var i=0;i<lenders.length;i++){
                        list += '<li><a href="' + lenders[i].url +'">'+
                                lenders[i].name + '</a>';
                    }
                    ad.innerHTML = 'ul' + list + 'ul';
                }
            }
        }
        
        
        function chart(principal,interest,monthly,payments){
            var graph = $('graph');
            graph.width = graph.width;            
            if(arguments.length==0|| !graph.getContext)return ;
            
            var g = graph.getContext('2d');
            var width = graph.width,
                height = graph.height;
                
            function paymentToX(n){
                return n*width/payments;
            }
            function amountToY(a){
                return height - (a*height/(monthly*payments*1.05));
            }
            
            g.moveTo(paymentToX(0),amountToY(0));
            g.lineTo(paymentToX(payments),amountToY(monthly*payments));
            g.lineTo(paymentToX(payments),amountToY(0));
            g.closePath();
            
            g.fillStyle = '#f88';
            g.fill();
            g.font="bold 12px sans-serif";
            g.fillText("Total Interest Payments",20,20);
            
            var equity = 0;
            g.beginPath();
            g.moveTo(paymentToX(0),amountToY(0));
            for(var  p=1;p<=payments;p++){
                var m = (principal - equity)*interest;
                equity += (monthly - m);
                g.lineTo(paymentToX(p),amountToY(equity));
            } 
            g.lineTo(paymentToX(payments),amountToY(0));
            g.closePath();
            g.fillStyle = 'green';
            g.fill();
            g.font="bold 12px sans-serif";
            g.fillText("Total Equity",20,35);
            
            
            var bal = principal;
            g.beginPath();
            g.moveTo(paymentToX(0),amountToY(bal));
            for(var  p=1;p<=payments;p++){
                var m = bal*interest;
                bal -= (monthly - m);
                g.lineTo(paymentToX(p),amountToY(bal));
            } 
            g.lineWidth = 1;
            g.stroke();            
            g.fillStyle = 'black';
            g.fillText("Total Balance",20,50);
            
            
            g.textAlign = 'center';
            var y = amountToY(0);
            for(var year=1; year*12<=payments;year++){
                var x = paymentToX(year*12);
                g.fillRect(x-0.5,y-3,1,3);
                if(year==1) g.fillText("Year",x,y-5);
                if(year % 5 ==0 && year *12 !== payments){
                    g.fillText(String(year),x,y-5);
                }
            }
            
            g.textAlign = "right";
            g.textBaseline = 'middle';
            var ticks = [ monthly * payments ,principal];
            var rightEdge = paymentToX(payments);
            for(var i=0;i<ticks.length;i++){
                var y = amountToY(ticks[i]);
                g.fillRect(rightEdge-3,y-0.5,3,1);
                g.fillText(String(ticks[i].toFixed(0)),rightEdge-5,y);
            }
        }
   
    
    </script>
</body>
</html>

运行效果：