如何在JavaScript中绕过一个数字?.toFixed()返回一个字符串?

Am I missing something here?

我是不是漏掉了什么?

var someNumber = 123.456;
someNumber = someNumber.toFixed(2);
alert(typeof(someNumber));
//alerts string

Why does .toFixed() return a string?

为什么.toFixed()返回一个字符串?

I want to round the number to 2 decimal digits.

我想把这个数四舍五入到两位小数。

10 个解决方案

#1

It returns a string because 0.1, and powers thereof (which are used to display decimal fractions), are not representable (at least not with full accuracy) in binary floating-point systems.

它返回一个字符串，因为在二进制浮点系统中，0。1和它的幂(用于显示十进制分数)是不可表示的(至少不是完全精确)。

For example, 0.1 is really 0.1000000000000000055511151231257827021181583404541015625, and 0.01 is really 0.01000000000000000020816681711721685132943093776702880859375. (Thanks to BigDecimal for proving my point. :-P)

例如，0。1是0。10000000000000000555111531257827021181583404541015625,0。01是0。010000000000000000208166817216851329430937702880859375。感谢BigDecimal证明了我的观点。:- p)

Therefore (absent a decimal floating point or rational number type), outputting it as a string is the only way to get it trimmed to exactly the precision required for display.

因此(没有十进制浮点数或有理数类型)，输出它作为字符串是使它精确裁剪到显示所需的精度的唯一方法。

#2

I've solved this problem by changing this:

我通过改变这个问题来解决这个问题:

someNumber = someNumber.toFixed(2)

...to this:

…:

someNumber = +someNumber.toFixed(2);

However this will convert the number to a string and parse it again, which will have a significant impact on performance. If you care about performance or type safety, check the the other answers as well.

但是，这将把数字转换为字符串并再次解析它，这将对性能产生重大影响。如果您关心性能或类型安全，请检查其他答案。

#3

Number.prototype.toFixed is a function designed to format a number before printing it out. It's from the family of toString, toExponential and toPrecision.

Number.prototype。toFixed是一种设计用来格式化数字然后打印出来的函数。它来自toString家族，指数级和toPrecision。

To round a number, you would do this:

对于整数，你可以这样做:

someNumber = 42.008;
someNumber = Math.round( someNumber * 1e2 ) / 1e2;
someNumber === 42.01;

// if you need 3 digits, replace 1e2 with 1e3 etc.

。

Or if you want a native-like function, here you are:

如果你想要一个类似于本机的函数，你可以这样做:

Number.prototype.toFixedNumber = function(x, base){
  var pow = Math.pow(base||10,x);
  return +( Math.round(this*pow) / pow );
}

someNumber = 42.008;
someNumber = someNumber.toFixedNumber(2);
someNumber === 42.01;


//or even hexadecimal

someNumber = 0xAF309/256  //which is af3.09
someNumber = someNumber.toFixedNumber(1, 16);
someNumber.toString(16) === "af3.1";

。

Tho I don't like jsperf that much, here's a link with comparsion of the method using conversion (in other answers) and this one:
https://jsperf.com/rounding-a-number-2

我不太喜欢jsperf，这里有一个使用转换(在其他答案中)的方法的比较链接，这个链接是https://jsperf.com/round- a-number-2

#4

Why not use parseFloat?

为什么不使用parseFloat吗?

var someNumber = 123.456;
someNumber = parseFloat(someNumber.toFixed(2));
alert(typeof(someNumber));
//alerts number

#5

Of course it returns a string. If you wanted to round the numeric variable you'd use Math.round() instead. The point of toFixed is to format the number with a fixed number of decimal places for display to the user.

当然它会返回一个字符串。如果想要对数值变量进行四舍五入，可以使用Math.round()。toFixed的要点是用一个固定的十进制位的数字格式显示给用户。

#6

I solved it with converting it back to number using JavaScript's Number() function

我通过使用JavaScript的number()函数将它转换回number来解决这个问题

var x = 2.2873424;
x = Number(x.toFixed(2));

#7

What would you expect it to return when it's supposed to format a number ? If you have a number you can't pretty much do anything with it because e.g.2 == 2.0 == 2.00 etc. so it has to be a string.

当它要格式化一个数字时，你希望它返回什么?如果你有一个数字，你几乎不能用它来做任何事情，因为。2 == 2.0 == 2.00等等，所以它必须是一个字符串。

#8

Because its primary use is displaying numbers? If you want to round numbers, use Math.round() with apropriate factors.

因为它的主要用途是显示数字?如果想要整数，可以使用Math.round()和固有因子。

#9

You can simply use a '+' to convert the result to a number.

您可以使用“+”将结果转换为数字。

var x = 22.032423;
x = +x.toFixed(2); // x = 22.03

#10

Here's a slightly more functional version of the answer m93a provided.

下面是m93a提供的稍微更实用的答案。

const toFixedNumber = (toFixTo = 2, base = 10) => num => {
  const pow = Math.pow(base, toFixTo)
  return +(Math.round(num * pow) / pow)
}

const oneNumber = 10.12323223

const result1 = toFixedNumber(2)(oneNumber) // 10.12
const result2 = toFixedNumber(3)(oneNumber) // 10.123

// or using pipeline-operator
const result3 = oneNumber |> toFixedNumber(2) // 10.12

#1