简单实现JS计算器功能

该计算器功能：
1.校验：小数点，重复计算，以及大量更符合用户体验的操作。
2.能够从键盘输入。

效果图：

html代码：

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
<link type="text/css" rel="stylesheet" href="css/style.css"></link>
</head>
<body>
  <!--定义按键表格,每个按键对应一个事件触发-->
  <div id="cal" class="cal">
    <form action="./calcuServlet" method="post" id="toCalcu">
      <div class="cont">
      <input id="upText" class="textShow" type="text" name="process"
         maxlength="10" readonly="readonly" />
      <input id="downText" class="text" type="text" name="text" value="0"
         maxlength="10" readonly="readonly" />  

      <input type="button" class="button" name="deleteAll" value="C" onclick="clearAllText()" />
      <input type="button" class="button" name="opposite" value="+/-" onclick="oppositeOp()" />
      <input type="button" class="button" name="delOne" value="←" onclick="deleteOneDigit()" />
      <input type="button" class="button" name="Add" value="+" onclick="clickOperation('+')" />
      <input type="button" class="button" name="seven" value="7" onclick="clickNum(7)" />
      <input type="button" class="button" name="eight" value="8" onclick="clickNum(8)" />
      <input type="button" class="button" name="nine" value="9" onclick="clickNum(9)" />
      <input type="button" class="button" name="Reduce" value="-" onclick="clickOperation('-')" />
      <input type="button" class="button" name="Four" value="4" onclick="clickNum(4)" />
      <input type="button" class="button" name="Five" value="5" onclick="clickNum(5)" />
      <input type="button" class="button" name="Sex" value="6" onclick="clickNum(6)" />
      <input type="button" class="button" name="Multip" value="x" onclick="clickOperation('x')" />
      <input type="button" class="button" name="One" value="1" onclick="clickNum(1)" />
      <input type="button" class="button" name="Two" value="2" onclick="clickNum(2)" />
      <input type="button" class="button" name="Three" value="3" onclick="clickNum(3)" />
      <input type="button" class="button" name="Division" value="÷" onclick="clickOperation('/')" />
      <input type="button" class="button" name="opposite" value="√" onclick="more()" />
      <input type="button" class="button" name="Zero" value="0" onclick="clickNum(0)" />
      <input type="button" class="button" name="Point" value="." onclick="clickNum('.')" />
      <input type="button" class="button" name="Equal" value="=" onclick="calcu()" />
      </div>
    </form> 

  </div>
  <div class="funcBtn">
    <input type="button" id="show" class="button" value="show" onclick="show()" /> <input
      type="button" id="hide" class="button" value="hide" onclick="hide()" />
  </div> 

<script type="text/javascript" src="./js/jquery-1.7.2.min.js"></script>
<script type="text/javascript" src="./js/calcu.js"></script>
</body>
</html>

css代码：

@CHARSET "UTF-8";
.button {
  width: 73px;
  height: 50px;
  margin-bottom: 5px;
  border: 1px solid #ddd;
  border-radius: 1px;
  font-weight: bold;
  color: #1e395b;
  background: aqua;
  font-size:20px;
  border-radius: 3px;
}
.text {
  width: 300px;
  border: 1px solid #c2c2c2;
  height: 50px;
  border-radius: 5px;
  font-size: 24px;
  text-align: right;
  background: #ffffff;
  margin-top: 10px;
  margin-bottom: 10px;
}
.textShow{
  width: 300px;
  border: 1px solid #c2c2c2;
  height: 40px;
  border-radius: 5px;
  font-size: 18px;
  text-align: right;
  background: #ffffff;
  margin-top: 10px;
  margin-bottom: 10px;
}
.cal{
margin-left:200px;
border:2px solid #99ccff;
margin:100px auto;
position:relative;
width:330px;
height:420px;
border-radius: 10px;
}
.cont{
 margin-left: 10px;
}
.funcBtn{
padding-left: 580px;
border-radius: 10px;
font-size: 20px;
position: fixed;
}

js代码：

/**
 *
 */
    var checkEqual = false;//Avoid repetition calcu
    var opFlag = false; //Check repetition add operation
    var upText = document.getElementById("upText");
    var cal = document.getElementById("cal").style;
    var downText = document.getElementById("downText"); 

    function show() {
      cal.display = "block";
    } 

    function hide() {
      cal.display = "none";
    } 

    function clearAllText() {
      upText.value = "";
      downText.value = "0";
      opFlag = false;
      checkEqual = false;
    } 

    function oppositeOp(){
      downText.value = -downText.value;
    } 

    function deleteOneDigit() {
      downText.value = downText.value.substring(0, downText.value.length - 1);
      if (downText.value == "" || (downText.value.charAt(0) == "-" && downText.value.charAt(1) == "")) {
        downText.value = "0";
        return downText.value;
      }
      return downText.value;
    } 

    function clickNum(num) {
      if(num == ".") {
        checkIfAddPoint(num);
      } else {
        checkIfAddNum(num);
      }
      checkEqual = false;
    } 

    function checkIfAddPoint(num) {
      if((num=="." && downText.value == "0") || opFlag == true) {
        downText.value="0.";
        opFlag = false;
      } else if(num == "." && downText.value.indexOf(".") > -1) {
        downText.value;
      } else {
        downText.value += num;
      }
    } 

    function checkIfAddNum(num) {
       if((num != "." && downText.value == "0" && downText.value[1] != ".")
           || opFlag == true
           || downText.value == "Infinity"
           || checkEqual == true) {
        downText.value = num;
        opFlag = false;
      } else {
        downText.value += num;
      }
    } 

    function clickOperation(op){
      checkEqual = false;
      downText.value = checkdownTextValid(downText.value);
      downText.value = checkZero(upText.value,downText.value);
      switch(op){
      case "+":{
        upText.value = appendupTextValue(upText.value,downText.value,"+");
        opFlag = true;
       }break;
      case "-":{
        upText.value = appendupTextValue(upText.value,downText.value,"-");
        opFlag = true;
       }break;
      case "x":{
        upText.value = appendupTextValue(upText.value,downText.value,"*");
        opFlag = true;
       }break;
      case "/":{
        upText.value = appendupTextValue(upText.value,downText.value,"/");
        opFlag = true;
       }break;
      }
    } 

    function checkdownTextValid(downText){
      if(downText.charAt(downText.length-1) == "."){
        return downText.substring(0,downText.length-1);
      }
      return downText;
    } 

    function checkZero(upText,downText){
      if(upText.charAt(upText.length-1) == "/" && downText == "0"){
        return "Error";
      }
      return downText;
    } 

    function appendupTextValue(oldvalue,newvalue,operation){
      if(oldvalue == ""){
         return oldvalue = newvalue+operation;
      } else if(opFlag!=true){
         return oldvaluee = oldvalue+newvalue+operation;
      } else{
        return oldvalue.substring(0, oldvalue.length-1)+operation;
      }
    } 

    function calcu() {
      if(!checkEqual){
      downText.value = eval(upText.value+downText.value);
      upText.value = "";
      checkEqual = true;
      }
    } 

    window.document.onkeydown = chooseKey;
    function chooseKey(evt){
      if(evt.keyCode == 13){alert("=");}
      else if(evt.keyCode == 8){deleteOneDigit();}
      else if(evt.keyCode == 27){clearAllText();}
      else if(evt.keyCode == 48){clickNum('0');}
      else if(evt.keyCode == 49){clickNum('1');}
      else if(evt.keyCode == 50){clickNum('2');}
      else if(evt.keyCode == 51){clickNum('3');}
      else if(evt.keyCode == 52){clickNum('4');}
      else if(evt.keyCode == 53){clickNum('5');}
      else if(evt.keyCode == 54){clickNum('6');}
      else if(evt.keyCode == 55){clickNum('7');}
      else if(evt.keyCode == 56){clickNum('8');}
      else if(evt.keyCode == 57){clickNum('9');}
      else if(evt.keyCode == 96){clickNum('0');}
      else if(evt.keyCode == 97){clickNum('1');}
      else if(evt.keyCode == 98){clickNum('2');}
      else if(evt.keyCode == 99){clickNum('3');}
      else if(evt.keyCode == 100){clickNum('4');}
      else if(evt.keyCode == 101){clickNum('5');}
      else if(evt.keyCode == 102){clickNum('6');}
      else if(evt.keyCode == 103){clickNum('7');}
      else if(evt.keyCode == 104){clickNum('8');}
      else if(evt.keyCode == 105){clickNum('9');}
      else if(evt.keyCode == 110){clickNum('.');}
      else if(evt.keyCode == 106){clickOperation('x');}
      else if(evt.keyCode == 107){clickOperation('+');}
      else if(evt.keyCode == 111){clickOperation('÷');}
      else if(evt.keyCode == 109){clickOperation('-');}

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