JavaScript 实现简易四则运算计算器示例

<!DOCTYPE html>
<html>
<meta name="content-type" content="text/html; charset=UTF-8">
<head>
  <title>www.jb51.net 计算器 Calculator</title>
  <!--将按键内容以字符串形式存储在文字框中当按钮为“=”时，调用eval方法计算结果然后将结果输出文字框中-->
  <script type="text/javascript">
    var numresult;
    var str;
    function onclicknum(nums) {
      str = document.getElementById("nummessege");
      str.value = str.value + nums;
    }
    function onclickclear() {
      str = document.getElementById("nummessege");
      str.value = "";
    }
    function onclickresult() {
      str = document.getElementById("nummessege");
      numresult = eval(str.value);
      str.value = numresult;
    }
  </script>
</head>
<body bgcolor="affff" >
<!--定义按键表格,每个按键对应一个事件触发-->
<table border="1" align="center" bgColor="#bbff77"
    style="height: 350px; width: 270px">
  <tr>
    <td colspan="4">
      <input type="text" id="nummessege"
          style="height: 90px; width: 350px; font-size: 50px" />
    </td>
  </tr>
  <tr>
    <td>
      <input type="button" value="1" id="1" onclick="onclicknum(1)"
          style="height: 70px; width: 90px; font-size: 35px">
    </td>
    <td>
      <input type="button" value="2" id="2" onclick="onclicknum(2)"
          style="height: 70px; width: 90px; font-size: 35px">
    </td>
    <td>
      <input type="button" value="3" id="3" onclick="onclicknum(3)"
          style="height: 70px; width: 90px; font-size: 35px">
    </td>
    <td>
      <input type="button" value="+" id="add" onclick="onclicknum('+')"
          style="height: 70px; width: 90px; font-size: 35px">
    </td>
  </tr>
  <tr>
    <td>
      <input type="button" value="4" id="4" onclick="onclicknum(4)"
          style="height: 70px; width: 90px; font-size: 35px">
    </td>
    <td>
      <input type="button" value="5" id="5" onclick="onclicknum(5)"
          style="height: 70px; width: 90px; font-size: 35px">
    </td>
    <td>
      <input type="button" value="6" id="6" onclick="onclicknum(6)"
          style="height: 70px; width: 90px; font-size: 35px">
    </td>
    <td>
      <input type="button" value="-" id="sub" onclick="onclicknum('-')"
          style="height: 70px; width: 90px; font-size: 35px">
    </td>
  </tr>
  <tr>
    <td>
      <input type="button" value="7" id="7" onclick="onclicknum(7)"
          style="height: 70px; width: 90px; font-size: 35px">
    </td>
    <td>
      <input type="button" value="8" id="8" onclick="onclicknum(8)"
          style="height: 70px; width: 90px; font-size: 35px">
    </td>
    <td>
      <input type="button" value="9" id="9" onclick="onclicknum(9)"
          style="height: 70px; width: 90px; font-size: 35px">
    </td>
    <td>
      <input type="button" value="*" id="mul" onclick="onclicknum('*')"
          style="height: 70px; width: 90px; font-size: 35px">
    </td>
  </tr>
  <tr>
    <td colspan="2">
      <input type="button" value="0" id="0" onclick="onclicknum(0)"
          style="height: 70px; width: 190px; font-size: 35px">
    </td>
    <td>
      <input type="button" value="." id="point" onclick="onclicknum('.')"
          style="height: 70px; width: 90px; font-size: 35px">
    </td>
    <td>
      <input type="button" value="/" id="division"
          onclick="onclicknum('/')"
          style="height: 70px; width: 90px; font-size: 35px">
    </td>
  </tr>
  <tr>
    <td colspan="2">
      <input type="button" value="Del" id="clear"
          onclick="onclickclear()"
          style="height: 70px; width: 190px; font-size: 35px" />
    </td>
    <td colspan="2">
      <input type="button" value="=" id="result"
          onclick="onclickresult()"
          style="height: 70px; width: 190px; font-size: 35px" />
    </td>
  </tr>
</table>
</body>
</html>