function calculator(){ var prices=document.getElementById("price"); var discounts=document.getElementById("number"); var pay; var select=document.getElementById("payfunction"); if((prices.value>=0&&!isNaN(prices.value))&&(discounts.value>=0&&!isNaN(discounts.value))&&prices.value!=""&&discounts.value!="") { pay=prices.value*discounts.value; switch(parseInt(select.value)){ case 1:pay=pay*0.5; break; case 2:pay=pay*0.8; break; case 3:pay=pay*0.6; break; } document.getElementById("result").value=pay; alert("恭喜你,交易成功!"); }else { prices.focus(); prices.select(); alert("请输入正确的价格和数量(也不能为空)!"); } } script>