实例 <!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>迷你计算器</title> <style type="text/css"> .box{ width:500px; height:200px; background-color:#efefef; border:1px solid lightgray; text-align:center; margin:20px auto; color:#636363; border-radius:15px; box-shadow:8px 8px 8px #999; } table{ margin:auto; border:1px solid blue;/*这框看得清楚*/ } td{ width:100px; height:30px; padding:5px 0px; border:1px solid red;/*这红框看得老清楚了,代码写到这儿计算按钮出去了,调了个参数*/ } input.select{ width:100%; height:100%; border:none; text-align:center; background-color:cyan; } button{ width:100%; height:100%; border:none; background-color:skyblue; color:white; } button:hover{ cursor:pointer; background-color: coral; width:105%; height:105%; } </style> </head> <body> <div class="box"> <h2>迷你计算器</h2> <form> <table> <tr> <td><input type="text" name="opt1" placeholder="操作数1"></td> <td> <select name="option"> <option value="null">请选择操作</option> <option value="add">+</option> <option value="sub">-</option> <option value="mul">*</option> <option value="div">/</option> </select> </td> <td><input type="text" name="opt2" placeholder="操作数2"></td> <td><button type="button">计算</button></td> </tr> <tr> <td colspan="2" align="right"><h3>结果:</h3></td> <td colspan="2" align="left"><h3 id="placeholder"></h3></td> </tr> </table> </form> </div> <script> //1.获取操作数,按钮与结果占位符 var opt1=document.getElementsByName('opt1')[0] var opt2=document.getElementsByName('opt2')[0] var opt=document.getElementsByName('option')[0] var btn=document.getElementsByTagName('button')[0] var placeholder=document.getElementById('placeholder') //2.已获取界面提交参数,执行计算操作 btn.onclick=function(){ var data1=parseFloat(opt1.value) var data2=parseFloat(opt2.value) if(opt1.value.length==0){ alert('第一个操作数不能为空') opt1.focus() return false }else if (isNaN(opt1.value)) { alert('第一个操作数必须为数字') opt1.focus() return false }else if(opt2.value.length==0){ alert('第二个操作数不能为空') opt2.focus() return false }else if(isNaN(opt2.value)){ alert('第二个操作数必须为数字') opt2.focus() return false }else{ var data1=parseFloat(opt1.value) var data2=parseFloat(opt2.value) } var option=opt.value var temp=0 var flag='' var result = '' switch (option){ case 'null': alert("请选择操作类型") opt.focus() return false case 'add': flag = '+' temp = data1 + data2 break case 'sub': flag = '-' temp = data1 - data2 break case 'mul': flag = '*' temp = data1 * data2 break case 'div': flag = '/' if (data2 == 0) { alert('除数不能为0,请重新输入') opt2.focus() return false } else { temp = data1 / data2 } break } var str = '<span style="color:coral">' str += data1+' '+flag+' '+data2 + ' = ' + temp str += '</span>' placeholder.innerHTML = str } </script> </body> </html> 运行实例 » 点击 "运行实例" 按钮查看在线实例