<!doctype html> <html> <head> <meta charset="utf-8"> <meta name="author" > <meta name="copyright" <title></title> <script> window.onload=function (){ var oTxt1=document.getElementById(‘txt1‘); var oTxt2=document.getElementById(‘txt2‘); var oBtn=document.getElementById(‘btn‘); var oSel=document.getElementById(‘sel1‘); oBtn.onclick=function (){ var _n1=oTxt1.value; var _n2=oTxt2.value; var n1=oTxt1.value-0; var n2=oTxt2.value-0; var str=oSel.value; if(_n1==‘‘|| _n2==‘‘) { alert(‘请输入‘); } else if(isNaN(n1)||isNaN(n2)) { alert(‘至少一个不是数字‘); } else { switch(str) { case ‘+‘: alert(n1+n2); break; case ‘-‘: alert(n1-n2); break; case ‘*‘: alert(n1*n2); break; case ‘-‘: alert(n1-n2); break; } } }; }; </script> </head> <body> <input type="text" id="txt1" /> <select id="sel1"> <option value="+">+</option> <option value="-">-</option> <option value="*">*</option> <option value="/">/</option> </select> <input type="text" id="txt2" /> <input type="button" value="计算" id="btn" /> </body> </html>
原文：http://www.cnblogs.com/heboliufengjie/p/4111102.html