DOM Project2:Loan Calculator

最新推荐文章于 2020-09-14 00:18:02 发布

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本文介绍了一个基于Bootstrap的贷款计算器的设计与实现。通过HTML、CSS和JavaScript，我们创建了一个用户友好的界面，用户可以输入贷款金额、利率和还款年限，系统将自动计算月供、总支付额和总利息。同时，引入了错误处理机制和加载动画，提升了用户体验。

HTML配置（bootstrap）

https://getbootstrap.com/docs/4.5/getting-started/introduction/

<!doctype html>
<html lang="en">
  <head>
    <!-- Required meta tags -->
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">

    <!-- Bootstrap CSS -->
    <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.5.0/css/bootstrap.min.css" integrity="sha384-9aIt2nRpC12Uk9gS9baDl411NQApFmC26EwAOH8WgZl5MYYxFfc+NcPb1dKGj7Sk" crossorigin="anonymous">

    <title>Hello, world!</title>
  </head>
  <body class="bg-dark">  <!-- //设置颜色 -->
    <div class="container">
      <div class="row">
        <div class="col-md-6 mx-auto">
          <div class="card card-body text-center mt-5">
            <h1 class="heading display-5 pb-3">Loan calculator</h1>
            <form id="loan-form">
              <div class="form-group">
                <div class="input-group">
                  <span class="input-group-text">$</span>
                  <input type="number" class="form-control" id="amount" placeholder="Loan Amount">
                </div>
              </div>
              <div class="form-group">
                <div class="input-group">
                  <span class="input-group-text">%</span>
                  <input type="number" class="form-control" id="interst" placeholder="Interest">
                </div>
              </div>
              <div class="form-group">
                <input type="number" class="form-control" id="years" placeholder="Year To Repay">
              </div>
              <div class="form-group">
                <input type="submit" value="Calculate" class="btn btn-dark btn-block">
              </div>
            </form>
            <!-- LOADER HERE-->
            <!--
            <div id="loading">
              <img src='img/loading.gif' alt="">
            </div>
          -->
            <!-- RESULTS-->
            <div id="results" class="pt-4">
              <h5>Results</h5>
              <div class="form-group">
                <div class="input-group">
                  <span class="input-group-text">Monthly Payment</span>
                  <input type="number" class="form-control" id="monthly-payment" disabled>
                </div>
              </div>
              <div class="form-group">
                <div class="input-group">
                  <span class="input-group-text">Total Payment</span>
                  <input type="number" class="form-control" id="total-payment" disabled>
                </div>
              </div>
              <div class="form-group">
                <div class="input-group">
                  <span class="input-group-text">Total Interest</span>
                  <input type="number" class="form-control" id="total-interest" disabled>
                </div>
              </div>
            </div>
          </div>
        </div>
      </div>
    </div>

    <!-- Optional JavaScript -->
    <!-- jQuery first, then Popper.js, then Bootstrap JS -->
    <script src="https://code.jquery.com/jquery-3.5.1.slim.min.js" integrity="sha384-DfXdz2htPH0lsSSs5nCTpuj/zy4C+OGpamoFVy38MVBnE+IbbVYUew+OrCXaRkfj" crossorigin="anonymous"></script>
    <script src="https://cdn.jsdelivr.net/npm/popper.js@1.16.0/dist/umd/popper.min.js" integrity="sha384-Q6E9RHvbIyZFJoft+2mJbHaEWldlvI9IOYy5n3zV9zzTtmI3UksdQRVvoxMfooAo" crossorigin="anonymous"></script>
    <script src="https://stackpath.bootstrapcdn.com/bootstrap/4.5.0/js/bootstrap.min.js" integrity="sha384-OgVRvuATP1z7JjHLkuOU7Xw704+h835Lr+6QL9UvYjZE3Ipu6Tp75j7Bh/kR0JKI" crossorigin="anonymous"></script>
    <script src="app.js"></script>
  </body>
</html>

在这里插入图片描述

设置计算公式——显示+warning

计算+显示结果
设定submit的event；
函数中得到所有input框；
取前三个计算；
给后三个赋值；

warining
若输入的数字不对，设置showerror函数；
即在title上面显示error；
settimeout设置函数，等待执行时间；

  //Insert error above heading
  card.insertBefore(errorDiv,heading);  //(要放入的parent，要放入的before)

  //clear error after 3sec
  setTimeout(clearError,3000); //3000ms后执行clearError

代码：

//listen for submit
document.getElementById('loan-form').addEventListener('submit',calculateresults);

//calculate result
function calculateresults(e){
  console.log('Calculating...');

  //UI Vars
  const amount = document.getElementById('amount');
  const interest=document.getElementById('interest');
  const years=document.getElementById("years");
  const monthlyPayment=document.getElementById("monthly-payment");
  const totalPayment=document.getElementById("total-payment");
  const totalInterest=document.getElementById("total-interest");

  //得到float类型
  const principal=parseFloat(amount.value);
  const calculatedInterest = parseFloat(interest.value) /100 /12;
  //计算interest
  const calculatedPayments= parseFloat(years.value)*12;

  //Compute monthly payment
  const x = Math.pow(1+calculatedInterest,calculatedPayments);
  const monthly = (principal*x*calculatedInterest)/(x-1);

  if(isFinite(monthly)){  //检查是否为无穷大，是则说明输入错误
    //给下面结果input赋值
    monthlyPayment.value=monthly.toFixed(2);//设定小数
    totalPayment.value=(monthly*calculatedPayments).toFixed(2);
    totalInterest.value=((monthly*calculatedPayments)-principal).toFixed(2);
  }else{
    showError("Please check your numbers");
  }

  e.preventDefault();
}

//Show Error
function showError(error){
  //Create a div
  const errorDiv=document.createElement('div');

  //Get elements
  const card=document.querySelector(".card");  //得到card
  const heading = document.querySelector(".heading"); //heding为title

  //Add class
  errorDiv.className="alert alert-danger"; //alert-danger设定样式，alert方便后续clear

  //Create text node and append to div
  errorDiv.appendChild(document.createTextNode(error));

  //Insert error above heading
  card.insertBefore(errorDiv,heading);  //(要放入的parent，要放入的before)

  //clear error after 3sec
  setTimeout(clearError,3000); //3000ms后执行clearError
}

//Clearerror
function clearError(){
  document.querySelector('.alert').remove();
}

在这里插入图片描述

加入延时——提高使用体验

（1）设定submit事件——传入函数；
隐藏结果+显示gif；
延时调用计算函数；

//listen for submit
document.getElementById('loan-form').addEventListener('submit',function(e){  //减慢calculateresults的输出
  //Hide results
  //先隐藏了，算出来再显示
  document.getElementById('results').style.display='none';

  //Show loader
  document.getElementById('loading').style.display='block';

  //延时
  setTimeout(calculateresults,2000);
  e.preventDefault();
});

（2）计算函数
计算并赋值；
成功显示结果，失败显示失败提示；

//calculate result
function calculateresults(e){
  //UI Vars
  const amount = document.getElementById('amount');
  const interest=document.getElementById('interest');
  const years=document.getElementById("years");
  const monthlyPayment=document.getElementById("monthly-payment");
  const totalPayment=document.getElementById("total-payment");
  const totalInterest=document.getElementById("total-interest");

  //得到float类型
  const principal=parseFloat(amount.value);
  const calculatedInterest = parseFloat(interest.value) /100 /12;
  //计算interest
  const calculatedPayments= parseFloat(years.value)*12;

  //Compute monthly payment
  const x = Math.pow(1+calculatedInterest,calculatedPayments);
  const monthly = (principal*x*calculatedInterest)/(x-1);

  if(isFinite(monthly)){  //检查是否为无穷大，是则说明输入错误
    //给下面结果input赋值
    monthlyPayment.value=monthly.toFixed(2);//设定小数
    totalPayment.value=(monthly*calculatedPayments).toFixed(2);
    totalInterest.value=((monthly*calculatedPayments)-principal).toFixed(2);
    //设置显示
    document.getElementById('results').style.display='block';
  }else{
    showError("Please check your numbers");
  }
  //隐藏gif
  document.getElementById('loading').style.display='none';
  //e.preventDefault();
}

（3）失败提示

//Show Error
function showError(error){
  //Create a div
  const errorDiv=document.createElement('div');

  //Get elements
  const card=document.querySelector(".card");  //得到card
  const heading = document.querySelector(".heading"); //heding为title

  //Add class
  errorDiv.className="alert alert-danger"; //alert-danger设定样式，alert方便后续clear

  //Create text node and append to div
  errorDiv.appendChild(document.createTextNode(error));

  //Insert error above heading
  card.insertBefore(errorDiv,heading);  //(要放入的parent，要放入的before)

  //clear error after 3sec
  setTimeout(clearError,3000); //3000ms后执行clearError
}

//Clearerror
function clearError(){
  document.querySelector('.alert').remove();
}