完美的js实现的计算器，带加减乘除号

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<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>计算器</title>
  <style>
      /*Basic reset*/
*{
  margin:0;
  padding:0;
  box-sizing: border-box;
  font: 14px Arial,sans-serif;
}
html{
  height:100%;
  background-color:lightslategrey;
}
 
#calculator{
  margin: 15px auto;
  width:330px;
  height:400px;
  border: 1px solid lightgray;
  background-color:darkgrey;
  padding:15px;
}
 
/*LOGO*/
.LOGO{
  height:20px;
 
}
.LOGO .name{
  float:left;
  line-height:30px;
}
.LOGO .verson{
  float:right;
  line-height:30px;
}
/*screen*/
#shuRu{
  margin-top:15px;
}
.screen{
  margin-top:5px;
  width:300px;
  height:40px;
  text-align: right;
  padding-right:10px;
  font-size:20px;
}
#keys{
  border:1px solid lightgray;
  height:223px;
  margin-top:25px;
  padding:8px;
}
#keys .last{
  margin-right:0px;
}
.footer{
  margin-top:20px;
  height:20px;
}
.footer .link{
  float:right;
}
 
#keys .buttons{
  float:left;
  width: 42px;
  height: 36px;
  text-align:center;
  background-color:lightgray;
  margin: 0 17px 20px 0;
}
  </style>
</head>
<body onload="onLoad()">
<div id="calculator">
  <div class="LOGO">
    <span class="name">简单的计算器</span>
    <span class="verson">@liumobai v1.0</span>
  </div>
  <div id="shuRu">
    <!--screen输入栏-->
    <div class="screen">
      <input type="text" id="screenName" name="screenName" class="screen" value="" onfocus="jsq(this)">
    </div>
  </div>
  <div id="keys">
    <!-- operators and other keys -->
    <!--第一排-->
    <input type="button" id="7" onclick="jsq(this.id)" value="7" class="buttons">
    <input type="button" id="8" onclick="jsq(this.id)" value="8" class="buttons">
    <input type="button" id="9" onclick="jsq(this.id)" value="9" class="buttons">
    <input type="button" id="Back" onclick="tuiGe()" value="Back" class="buttons">
    <input type="button" id="C" onclick="clearNum()" value="C" class="buttons" style="margin-right:0px">
    <!--第二排-->
    <input type="button" id="4" onclick="jsq(this.id)" value="4" class="buttons">
    <input type="button" id="5" onclick="jsq(this.id)" value="5" class="buttons">
    <input type="button" id="6" onclick="jsq(this.id)" value="6" class="buttons">
    <input type="button" id="*" onclick="jsq(this.id)" value="*" class="buttons">
    <input type="button" id="/" onclick="jsq(this.id)" value="/" class="buttons" style="margin-right:0px">
    <!--第三排-->
    <input type="button" id="1" onclick="jsq(this.id)" value="1" class="buttons">
    <input type="button" id="2" onclick="jsq(this.id)" value="2" class="buttons">
    <input type="button" id="3" onclick="jsq(this.id)" value="3" class="buttons">
    <input type="button" id="+" onclick="jsq(this.id)" value="+" class="buttons">
    <input type="button" id="-" onclick="jsq(this.id)" value="-" class="buttons" style="margin-right:0px">
    <!--第四排-->
    <input type="button" id="0" onclick="jsq(this.id)" value="0" class="buttons">
    <input type="button" id="00" onclick="jsq(this.id)" value="00" class="buttons">
    <input type="button" id="." onclick="jsq(this.id)" value="." class="buttons">
    <input type="button" id="%" onclick="jsq(this.id)" value="%" class="buttons">
    <input type="button" id="eva" onclick="eva()" value="=" class="buttons" style="margin-right:0px">
  </div>
  <div class="footer">
    <span class="aside">欢迎使用javascript计算器</span>
      <span class="link">
        <a href="#" title="声明" target="_blank">反馈</a>
      </span>
  </div>
</div>
<script>
  var num = 0; // 定义第一个输入的数据
  function jsq(num) {
    //获取当前输入
    document.getElementById(‘screenName‘).value += document.getElementById(num).value;
  }
  function eva() {
    //计算输入结果
    document.getElementById("screenName").value = eval(document.getElementById("screenName").value);
  }
  function clearNum() {
    //清0
    document.getElementById("screenName").value = null;
    document.getElementById("screenName").focus();
  }
  function tuiGe() {
    //退格
    var arr = document.getElementById("screenName");
    arr.value = arr.value.substring(0, arr.value.length - 1);
  }
  function onLoad(){
    //加载完毕后光标自动对应到输入框
    document.getElementById("screenName").focus();
  }
</script>
</body>
</html>

 

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