js 浮点运算出现的精度丢失问题

var myf='6.202555';

myf=Number(myf).toFixed(2);//使用方法

Number.prototype.toFixed = function(scale) {
var s = this + "";
if (!scale) scale = 0;
if (s.indexOf(".") == -1) s += ".";
s += new Array(scale + 1).join("0");
if (new RegExp("^(-|\\+)?(\\d+(\\.\\d{0," + (scale + 1) + "})?)\\d*$").test(s)) {

var s = "0" + RegExp.$2, pm = RegExp.$1, a = RegExp.$3.length, b = true;
if (a == scale + 2)  {
a = s.match(/\d/g);
if (parseInt(a[a.length - 1]) > 4) {
for (var i = a.length - 2; i >= 0; i--) {
a[i] = parseInt(a[i]) + 1;
if (a[i] == 10) {
a[i] = 0;
b = i != 1;
}else {
break;
}
}
}

s = a.join("").replace(new RegExp("(\\d+)(\\d{" + scale + "})\\d$"), "$1.$2");
}
if (b){
s = s.substr(1);
}
return (pm + s).replace(/\.$/, "");
}
return this + "";
}