JS 浮点值精确计算

from:http://rockyee.iteye.com/blog/891538

 1 Number.prototype.toFixed = function(scale){  
 2         var s = this + "";  
 3         if (!scale) scale = 0;  
 4         if (s.indexOf(".") == -1) s += ".";  
 5         s += new Array(scale + 1).join("0");  
 6         if (new RegExp("^(-|\\+)?(\\d+(\\.\\d{0," + (scale + 1) + "})?)\\d*$").test(s))  
 7         {  
 8             var s = "0" + RegExp.$2, pm = RegExp.$1, a = RegExp.$3.length, b = true;  
 9             if (a == scale + 2)  
10             {  
11                 a = s.match(/\d/g);  
12                 if (parseInt(a[a.length - 1]) > 4)  
13                 {  
14                     for (var i = a.length - 2; i >= 0; i--)  
15                     {  
16                         a[i] = parseInt(a[i]) + 1;  
17                         if (a[i] == 10)  
18                         {  
19                             a[i] = 0;  
20                             b = i != 1;  
21                         }  
22                         else  
23                             break;  
24                     }  
25                 }  
26                 s = a.join("").replace(new RegExp("(\\d+)(\\d{" + scale + "})\\d$"), "$1.$2");  
27             }  
28             if (b) s = s.substr(1);  
29             return (pm + s).replace(/\.$/, "");  
30         }  
31         return this + "";  
32 }

通过正则来四舍五入，覆盖Number原本的toFixed方法

测试：

alert(Number(9.13-9.02));

alert(Number(9.13-9.02).toFixed(2));