<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>js从入门到放弃</title>
</head>
<body>
<input type="text" id="txt" />
<select id="fuhao">
<option>+</option>
<option>-</option>
<option>*</option>
<option>/</option>
</select>
<input type="text" id="txt1" />
<input type="button" value="=" onclick="return jisuan()" />
<input type='text' id='txt2' >
<script type="text/javascript">
function jisuan()
{
var txt=document.getElementById('txt').value;
var txt1=document.getElementById('txt1').value;
var txt2=document.getElementById('txt2');
var fuhao=document.getElementById('fuhao').value;
if(fuhao=='+')
{
var sum=parseInt(txt)+parseInt(txt1);
txt2.value=sum;
}
else if(fuhao=='-')
{
var sum=parseInt(txt)-parseInt(txt1);
txt2.value=sum;
}
else if(fuhao=='*')
{
var sum=parseInt(txt)*parseInt(txt1);
txt2.value=sum;
}
else
{
var sum=parseInt(txt)/parseInt(txt1);
txt2.value=sum;
}
}
</script>
</body>
</html>简单方法：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>a.html</title>
</head>
<body>
<script>
function fun(){
var one=document.getElementById('one').value;
var two=document.getElementById('two').value;
var fuhao=document.getElementById('fuhao').value;
var sum=eval(one+fuhao+two);
document.getElementById('sum').value=sum;
}
</script>
<input type="text" id='one' />
<select id='fuhao'>
<option value='+'>＋</option>
<option value='-'>-</option>
<option value='*'>*</option>
<option value='/'>/</option>
</select>
<input type='text' id='two' />
<input type='button' value='=' onclick='return fun()' />
<input type='text' id='sum' />
</body>
</html>