用js制作简易计算机有没有会的

img

你哪一步不会？


<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title>改善简易计算器</title>
        <script type="text/javascript">
            function compute(obj) { //obj 为形式参数，它代表运算符号
                let num1, num2;
                num1 = Number(document.getElementById("txtNum1").value);
                num2 = Number(document.getElementById("txtNum2").value);
                let result;
                if(isNaN(num1)||isNaN(num2))
                {
                    alert("输入的数字有误，请重新输入！");
                }
                else
                {
                    switch(obj) {
                    case "+":
                        result = num1 + num2;
                        break;
                    case "-":
                        result = num1 - num2;
                        break;
                    case "*":
                        result = num1 * num2;
                        break;
                    case "/":
                        if(num2===0)
                            alert("除数不能为0");
                        else
                        {
                            result = num1 / num2;
                            break;
                        }                        
                    }
                    document.getElementById("txtResult").value=result;
                }                
            }
        </script>
    </head>

    <body>
        <form action="" method="post" id="myform" name="myform">
            <table border="0">
                <tr>
                    
                    <td colspan="3">
                        <h3>改善简易计算器</h3>
                    </td>
                </tr>
                <tr>
                    <td>第一个数</td>
                    <td colspan="3">
                        <input name="txtNum1" type="text" id="txtNum1" size="25">
                    </td>
                </tr>
                <tr>
                    <td>第二个数</td>
                    <td colspan="3">
                        <input name="txtNum2" type="text" id="txtNum2" size="25">
                    </td>
                </tr>
                <tr>
                    <td>
                        <input name="addButton2" type="button" id="addButton2" value="  ＋  " onClick="compute('+')">
                    </td>
                    <td>
                        <input name="subButton2" type="button" id="subButton2" value="  －  " onClick="compute('-')">
                    </td>
                    <td>
                        <input name="mulButton2" type="button" id="mulButton2" value="  ×  " onClick="compute('*')">
                    </td>
                    <td>
                        <input name="divButton2" type="button" id="divButton2" value="  ÷  " onClick="compute('/')">
                    </td>
                </tr>
                <tr>
                    <td>计算结果</td>
                    <td colspan="3">
                        <input name="txtResult" type="text" id="txtResult" size="25">
                    </td>
                </tr>
            </table>
        </form>
    </body>

</html>

计算机和计算器一个字，差距好大