<html>
<script>
function round (n, d) {
var t = n < 0 ? "-":"";
n = Math.abs(n) - 0;
d = d || 2;
var f = Math.pow(10, d);
n = Math.round(n * f) / f;
n += Math.pow(10, - (d + 1));
n += '';
return d == 0 ? t+n.substring(0, n.indexOf('.')) :
t+n.substring(0, n.indexOf('.') + d + 1);
}
</script>
<body><script type="text/javascript">
document.writeln(round(3.65*97/100,3));
document.writeln(round(3.65*(97/100),3));document.writeln(round(0.435*90/100,3));
document.writeln(round(0.435*(90/100),3));</script>
</body>
</html>
按正常的四舍五入，正确答案应该是1，4
现在问题出来了，我到底应该按哪种运算顺序来呢？
JS银行家JS 银行家浮点运算四舍五入
<html>
<script>
function round (n, d0) {
var d = d0+1;
var t = n < 0 ? "-":"";
n = Math.abs(n) - 0;
d = d || 2;
var f = Math.pow(10, d);
n = Math.round(n * f) / f;
n += Math.pow(10, - (d + 1));
n += '';
return d == 0 ? t+n.substring(0, n.indexOf('.')) :
t+n.substring(0, n.indexOf('.') + d + 1);
}
</script>
<body>
<script type="text/javascript">
document.writeln(round(3.65*97/100,3));
document.writeln(round(3.65*(97/100),3));
document.writeln(round(0.435*90/100,3));
document.writeln(round(0.435*(90/100),3));
</script>
</body>
</html>
之后：运行结果是3.5405 3.5405 0.3915 0.3915
尽量避开浮点数乘除，其中涉及到小数转换成二进制的失真。
（其实我认为就像无限循环小数，要用无穷多为才能表示，计算机又没有那么多位，肯定会失真了）