javaScript实现-在两个文本框中输入值计算加减乘除法结果显示在另一个文本框中

在两个文本框中输入值计算加减乘除法结果显示在另一个文本框中。<!DOCTYPE html><html lang="en"><head><meta charset="UTF-8"><meta http-equiv="X-UA-Compatible" content="IE=edge"><meta name="viewport" con

初遇见

8061人浏览 · 2021-06-06 13:17:57

初遇见 · 2021-06-06 13:17:57 发布

在两个文本框中输入值计算加减乘除法结果显示在另一个文本框中。
在这里插入图片描述

方法一：用if - else

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
 
</head>
<body>
    <input id="n1">
    <select  id="flag">
        <option value="+">+</option>
        <option value="-">-</option>
        <option value="*">*</option>
        <option value="/">/</option>
    </select>
    <input id="n2">
    <button onclick="sum()">=</button>
    <input id="n3" >
<script>
 //取下拉框的选中项的value
 function sum()
   {
    var one = document.getElementById("n1");
    var two = document.getElementById("n2");
    var three = document.getElementById("n3");
    //判断传入的符号
    if(flag.value == '+'){
        three.value=  parseInt(one.value)+parseInt(two.value);//将计算的结果显示在另一个文本框内
    }else if(flag.value == '-'){
        three.value= parseInt(one.value)-parseInt(two.value);
    }else if(flag.value == '*'){
        three.value=  parseInt(one.value)*parseInt(two.value);
    }else if(flag.value == '/'){
        if(two.value==0){
            alert("除数不能为0！！！");
        }else{
            three.value=  parseInt(one.value)/parseInt(two.value);
        }
    }
}
</script>
</body>
</html>

方法二：动态的获取

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>用文本框输入数字计算加减乘除法结果显示在另一个文本框</title>
</head>
<body>
    <input id="n1">
    <select  id="flag">
        <option value="+">+</option>
        <option value="-">-</option>
        <option value="*">*</option>
        <option value="/">/</option>
    </select>
    <input id="n2">
    <button onclick="test()">=</button>
    <input id="n3">
<script>
 //取下拉框的选中项的value
function test(){
    //取输出的值
    var n1 = document.getElementById("n1").value;
    var n2 = document.getElementById("n2").value;
    //取下拉框架选中的value
    var flag = document.getElementById("flag").value;
    var result = "var a = parseInt(n1);var b = parseInt(n2); return a"+flag+"b";
    var fun = new Function("n1","n2",result);
    var n3 = fun(n1,n2);
    document.getElementById("n3").value = n3;
}
</script>
</body>
</html>

方法三：用eval()
eval(字符串) 将参数字符串做为一个javascript表达式进行执行,用它可以生成一些动态的javascript表达式。

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    </head>
    <body>
        <input id="n1"  value="" />
        <select id="flag">
            <option value="+">+</option>
            <option value="-">-</option>
            <option value="*">*</option>
            <option value="/">/</option>
        </select>
        <input id="n2" value=""  />
        <button onclick="test()">=</button>
        <input id="n3" />

        <script>
            function test(){
                var n1=parseFloat(document.getElementById("n1").value);
                var n2=parseFloat(document.getElementById("n2").value);
                var flag=document.getElementById("flag").value;	
                var result=eval(parseFloat(n1)+flag+parseFloat(n2));
                document.getElementById('n3').value=result;       
            }
        </script>
    </body> 
</html>