<!DOCTYPE html>
<html>
<head>
<title> 事件</title>
<script type="text/javascript">
function count(){
//获取第一个输入框的值
var txt1 = document.getElementById("txt1").value;
//获取第二个输入框的值
var txt2 = document.getElementById("txt2").value;
//获取选择框的值
var sign = document.getElementById("select").value;
//获取通过下拉框来选择的值来改变加减乘除的运算法则
var regex="^[0-9]*([\.]{0,1}[0-9]*)$";
//正浮点数正则
//var regex = "[1-9]\d*.\d*|0.\d*[1-9]\d*";
if(!txt1.match(regex) || !txt2.match(regex)){
alert("请输入数字!");
}else{
var result;
switch(sign){
case "+":result=parseFloat(txt1)+parseFloat(txt2);
break;
case "-":result=parseFloat(txt1)-parseFloat(txt2);
break;
case "*":result=parseFloat(txt1)*parseFloat(txt2);
break;
case "/":result=parseFloat(txt1)/parseFloat(txt2);
break;
default:alert("无效运算!");
break;
}
//设置结果输入框的值
document.getElementById("fruit").value=result;
}
}
</script>
</head>
<body>
<input type='text' id='txt1' />
<select id='select'>
<option value='+'>+</option>
<option value="-">-</option>
<option value="*">*</option>
<option value="/">/</option>
</select>
<input type='text' id='txt2' />
<input type='button' value=' = ' onclick="count()"/> <!--通过 = 按钮来调用创建的函数，得到结果-->
<input type='text' id='fruit' />
</body>
</html>
var regex ="^([1-9]\\d*(\\.\\d*[1-9])?)|(0\\.\\d*[1-9])$"