如何在負數時顯示警報消息

Question

即時通訊在javascript中是noob，並且想知道當總值低於0時如何顯示警報消息。有問題的頁面在這裏（http://cashmoneypaid.com/order-form-phones-work）以及我嘗試過的腳本如下。非常感謝幫忙。

function checkTotal() { 
    document.listForm.total.value = ''; 
    var sum = 20; 
    for (i = 0; i < document.listForm.choice.length; i++) { 
     if (document.listForm.choice[i].checked) { 
      sum = sum + parseInt(document.listForm.choice[i].value); 
     } 
    } 
    document.listForm.total.value = sum; 
} 
$("#total").ready(function() { 
    if (sum > 0) { 
     alert("We are sorry, but at this time we can not offer you any money for your item"); 
    } 
});​ 

Answer 1

既然您使用jQuery改變它一切！

$(function(){ 
    var sum = 20; 
    $('form input[type="checkbox"]').change(function(){ 
     if (this.checked) 
      sum -= parseFloat(this.value); 
     else 
      sum += parseFloat(this.value); 

     if (sum < 0) 
      alert('bla bla bla'); 
    }); 
}); 

Live DEMO

您也可以使用這一招：

$('form input[type="checkbox"]').change(function(){ 
    var value = parseFloat(this.value) * (this.checked ? -1 : 1); 
    sum += value  
    ... 

Live DEMO