JavaScript数学，舍入到小数点后两位 [英] JavaScript math, round to two decimal places

问题描述

我有以下JavaScript语法：

I have the following JavaScript syntax:

var discount = Math.round(100 - (price / listprice) * 100);

这会累计到整数。如何以两位小数返回结果？

This rounds up to the whole number. How can I return the result with two decimal places?

推荐答案

注意 - 如果3位精度很重要，请参阅编辑4

var discount = (price / listprice).toFixed(2);

toFixed会根据超过2位小数的值向上或向下舍入。

toFixed will round up or down for you depending on the values beyond 2 decimals.

示例： http://jsfiddle.net/calder12/tv9HY/

文档： https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/toFixed

编辑 - 正如其他人所说，这会将结果转换为字符串。为了避免这种情况：

Edit - As mentioned by others this converts the result to a string. To avoid this:

var discount = +((price / listprice).toFixed(2));

编辑2 - 正如评论中所提到的，这个功能在某些方面失败了精度，例如在1.005的情况下，它将返回1.00而不是1.01。如果这个程度的准确性很重要我找到了答案： https://stackoverflow.com/a/32605063/1726511这似乎与我尝试的所有测试都很好。

Edit 2- As also mentioned in the comments this function fails in some precision, in the case of 1.005 for example it will return 1.00 instead of 1.01. If accuracy to this degree is important I've found this answer: https://stackoverflow.com/a/32605063/1726511 Which seems to work well with all the tests I've tried.

虽然需要一个小的修改，上面链接的答案中的函数返回整数时它舍入到一，所以例如99.004将返回99而不是99.00，这不是显示价格的理想选择。

There is one minor modification required though, the function in the answer linked above returns whole numbers when it rounds to one, so for example 99.004 will return 99 instead of 99.00 which isn't ideal for displaying prices.

编辑3 - 似乎有实际返回的toFixed是STILL搞砸了一些数字，这个最终的编辑似乎工作。 Geez这么多的返工！

Edit 3 - Seems having the toFixed on the actual return was STILL screwing up some numbers, this final edit appears to work. Geez so many reworks!

   var discount = roundTo((price / listprice), 2);

   function roundTo(n, digits) {
     if (digits === undefined) {
       digits = 0;
     }

     var multiplicator = Math.pow(10, digits);
     n = parseFloat((n * multiplicator).toFixed(11));
     var test =(Math.round(n) / multiplicator);
     return +(test.toFixed(digits));
   }

请参阅此处的小提琴示例： https://jsfiddle.net/calder12/3Lbhfy5s/

See Fiddle example here: https://jsfiddle.net/calder12/3Lbhfy5s/

编辑4 - 你们是在杀我编辑3在负数上失败，没有深入研究为什么在进行四舍五入之前处理将负数转为正数然后在返回结果之前将其转回来更容易。

Edit 4 - You guys are killing me. Edit 3 fails on negative numbers, without digging into why it's just easier to deal with turning a negative number positive before doing the rounding, then turning it back before returning the result.

function roundTo(n, digits) {
    var negative = false;
    if (digits === undefined) {
        digits = 0;
    }
        if( n < 0) {
        negative = true;
      n = n * -1;
    }
    var multiplicator = Math.pow(10, digits);
    n = parseFloat((n * multiplicator).toFixed(11));
    n = (Math.round(n) / multiplicator).toFixed(2);
    if( negative ) {    
        n = (n * -1).toFixed(2);
    }
    return n;
}

小提琴： https://jsfiddle.net/3Lbhfy5s/79/

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