blocks|key|1244726|text|因为只有两个小数位数，所以没有“精确”的财务计算，但这是一个更普遍的问题。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1244727|在JavaScript中，您可以按100缩放每个值，并在每次出现分数时使用Math.round()。|offset|length|style|CODE|1244728|您可以使用对象来存储数字，并在其原型valueOf()方法中包含舍入。如下所示：|1244729|sys+=+require('sys');

var+Money+=+function(amount)+{
++++++++this.amount+=+amount;
++++}
Money.prototype.valueOf+=+function()+{
++++return+Math.round(this.amount*100)/100;
}

var+m+=+new+Money(50.42355446);
var+n+=+new+Money(30.342141);

sys.puts(m.amount+%2B+n.amount);+//80.76569546
sys.puts(m%2Bn);+//80.76|code-block|syntax|javascript|1244730|这样，每次您使用货币对象时，它将被表示为四舍五入为两个小数。未四舍五入的值仍然可以通过m.amount访问。|1244731|如果您愿意，您可以在Money.prototype.valueOf()中内置您自己的舍入算法。|1244732|entityMap^0|0|11|C|0|I|9|0|0|17|8|0|A|P|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|V|8|@$D|W|E|X|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|Y|8|@$D|Z|E|10|F|G]]|9|@]|A|$]]|$1|J|3|K|5|L|7|11|8|@]|9|@]|A|$M|N]]|$1|O|3|P|5|6|7|12|8|@$D|13|E|14|F|G]]|9|@]|A|$]]|$1|Q|3|R|5|6|7|15|8|@$D|16|E|17|F|G]]|9|@]|A|$]]|$1|S|3|-4|5|6|7|18|8|@]|9|@]|A|$]]]|T|$]]

There's no such thing as "precise" financial calculation because of just two decimal fraction digits but that's a more general problem.

In JavaScript, you can scale every value by 100 and use <code>Math.round()</code> everytime a fraction can occur.

You could use an object to store the numbers and include the rounding in its prototypes <code>valueOf()</code> method. Like this:

<pre><code>sys = require('sys');

var Money = function(amount) {
 this.amount = amount;
 }
Money.prototype.valueOf = function() {
 return Math.round(this.amount*100)/100;
}

var m = new Money(50.42355446);
var n = new Money(30.342141);

sys.puts(m.amount + n.amount); //80.76569546
sys.puts(m+n); //80.76
</code></pre>

That way, everytime you use a Money-object, it will be represented as rounded to two decimals. The unrounded value is still accessible via <code>m.amount</code>.

You can build in your own rounding algorithm into <code>Money.prototype.valueOf()</code>, if you like.

blocks|key|1029878|text|将每个值按100缩放是解决方案。手工操作可能是无用的，因为您可以找到为您做这件事的库。我推荐moneysafe，它提供了一个非常适合ES6应用程序的函数式API：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1029879|const+{+in$,+$+}+=+require('moneysafe');
console.log(in$($(10.5)+%2B+$(.3));+//+10.8|code-block|syntax|javascript|1029880|https://github.com/ericelliott/moneysafe|offset|length|1029881|在Node.js和浏览器中均可使用。|1029882|entityMap|0|LINK|mutability|MUTABLE|url^0|0|0|0|14|0|0|0^^$0|@$1|2|3|4|5|6|7|T|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|U|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|V|8|@]|9|@$I|W|J|X|1|Y]]|A|$]]|$1|K|3|L|5|6|7|Z|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|10|8|@]|9|@]|A|$]]]|N|$O|$5|P|Q|R|A|$S|H]]]]

Scaling every value by 100 is the solution. Doing it by hand is probably useless, since you can find libraries that do that for you. I recommend moneysafe, which offers a functional API well suited for ES6 applications:

<pre><code>const { in$, $ } = require('moneysafe');
console.log(in$($(10.5) + $(.3)); // 10.8
</code></pre>

<a href="https://github.com/ericelliott/moneysafe" rel="noreferrer">https://github.com/ericelliott/moneysafe</a>

Works both in Node.js and the browser.

blocks|key|1244819|text|使用decimaljs这是一个非常好的库，它解决了这个问题的一个苛刻的部分……|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1244820|只要在你的所有操作中使用它。|1244821|https://github.com/MikeMcl/decimal.js/|offset|length|1244822|entityMap|0|LINK|mutability|MUTABLE|url^0|0|0|0|12|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|Q|8|@]|9|@$F|R|G|S|1|T]]|A|$]]|$1|H|3|-4|5|6|7|U|8|@]|9|@]|A|$]]]|I|$J|$5|K|L|M|A|$N|E]]]]

use decimaljs ... It a very good library that solves a harsh part of the problem ... 

just use it in all your operation. 

<a href="https://github.com/MikeMcl/decimal.js/" rel="nofollow noreferrer">https://github.com/MikeMcl/decimal.js/</a>

blocks|key|1244874|text|由于其编码的二进制性质，一些十进制数不能完全准确地表示。例如|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1244875|var+money+=+600.90;
var+price+=+200.30;
var+total+=+price+*+3;

//+Outputs:+false
console.log(money+>=+total);

//+Outputs:+600.9000000000001
console.log(total);|code-block|syntax|javascript|1244876|如果你需要使用纯javascript，那么你需要考虑每一次计算的解决方案。对于上面的代码，我们可以将小数转换为整数。|1244877|var+money+=+60090;
var+price+=+20030;
var+total+=+price+*+3;

//+Outputs:+true
console.log(money+>=+total);

//+Outputs:+60090
console.log(total);|1244878|Avoiding+Problems+with+Decimal+Math+in+JavaScript|offset|length|1244879|有一个专用于财务计算的库，其中包含大量的文档。Finance.js|1244880|entityMap|0|LINK|mutability|MUTABLE|url|http://adripofjavascript.com/blog/drips/avoiding-problems-with-decimal-math-in-javascript.html|1|http://financejs.org/^0|0|0|0|0|0|1D|0|0|N|A|1|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|11|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|12|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|13|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|14|8|@]|9|@$M|15|N|16|1|17]]|A|$]]|$1|O|3|P|5|6|7|18|8|@]|9|@$M|19|N|1A|1|1B]]|A|$]]|$1|Q|3|-4|5|6|7|1C|8|@]|9|@]|A|$]]]|R|$S|$5|T|U|V|A|$W|X]]|Y|$5|T|U|V|A|$W|Z]]]]

Due to the binary nature of their encoding, some decimal numbers cannot be represented with perfect accuracy. For example

<pre><code>var money = 600.90;
var price = 200.30;
var total = price * 3;

// Outputs: false
console.log(money &gt;= total);

// Outputs: 600.9000000000001
console.log(total);
</code></pre>

If you need to use pure javascript then you have need to think about solution for every calculation. For above code we can convert decimals to whole integers.

<pre><code>var money = 60090;
var price = 20030;
var total = price * 3;

// Outputs: true
console.log(money &gt;= total);

// Outputs: 60090
console.log(total);
</code></pre>

<a href="http://adripofjavascript.com/blog/drips/avoiding-problems-with-decimal-math-in-javascript.html" rel="nofollow noreferrer">Avoiding Problems with Decimal Math in JavaScript</a>

There is a dedicated library for financial calculations with great documentation. <a href="http://financejs.org/" rel="nofollow noreferrer">Finance.js</a>

blocks|key|1030016|text|不幸的是，到目前为止所有的答案都忽略了一个事实，即并不是所有的货币都有100个子单位(例如，美分是美元的子单位)。像伊拉克第纳尔(IQD)这样的货币有1000个子单位:一个伊拉克第纳尔有1000个文件。日元(JPY)没有子单位。所以“乘以100来做整数运算”并不总是正确的答案。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1030017|此外，对于货币计算，您还需要跟踪货币。您不能在印度卢比(INR)中添加美元(USD)+(除非先将一个卢比转换为另一个)。|1030018|JavaScript的integer数据类型可以表示的最大数量也有限制。|1030019|在货币计算中，您还必须记住，货币的精度是有限的(通常是0-3个小数点)&需要以特定的方式进行舍入(例如，“正常”舍入与银行家的舍入)。要执行的舍入类型也可能因司法辖区/货币而异。|1030020|How+to+handle+money+in+javascript对相关的观点进行了很好的讨论。|offset|length|1030021|在我的搜索中，我找到了addresses+many+of+the+issues+wrt+monetary+calculations的dinero.js库。我还没有在生产系统中使用它，所以不能给出一个有见地的意见。|1030022|entityMap|0|LINK|mutability|MUTABLE|url|https://medium.com/@magnusjt/how-to-handle-money-in-javascript-b954d612373c|1|https://frontstuff.io/how-to-handle-monetary-values-in-javascript|2|https://dinerojs.com/^0|0|0|0|0|0|X|0|0|B|1I|1|1U|9|2|0^^$0|@$1|2|3|4|5|6|7|Z|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|10|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|11|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|12|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|13|8|@]|9|@$J|14|K|15|1|16]]|A|$]]|$1|L|3|M|5|6|7|17|8|@]|9|@$J|18|K|19|1|1A]|$J|1B|K|1C|1|1D]]|A|$]]|$1|N|3|-4|5|6|7|1E|8|@]|9|@]|A|$]]]|O|$P|$5|Q|R|S|A|$T|U]]|V|$5|Q|R|S|A|$T|W]]|X|$5|Q|R|S|A|$T|Y]]]]

Unfortunately all of the answers so far ignore the fact that not all currencies have 100 sub-units (e.g., the cent is the sub-unit of the US dollar (USD)). Currencies like the Iraqi Dinar (IQD) have 1000 sub-units: an Iraqi Dinar has 1000 fils. The Japanese Yen (JPY) has no sub-units. So "multiply by 100 to do integer arithmetic" isn't always the correct answer.

Additionally for monetary calculations you also need to keep track of the currency. You can't add a US Dollar (USD) to an Indian Rupee (INR) (without first converting one to the other).

There are also limitations on the maximum amount that can be represented by JavaScript's integer data type.

In monetary calculations you also have to keep in mind that money has finite precision (typically 0-3 decimal points) &amp; rounding needs to be done in particular ways (e.g., "normal" rounding vs. banker's rounding). The type of rounding to be performed might also vary by jurisdiction/currency.

<a href="https://medium.com/@magnusjt/how-to-handle-money-in-javascript-b954d612373c" rel="nofollow noreferrer">How to handle money in javascript</a> has a very good discussion of the relevant points.

In my searches I found the <a href="https://dinerojs.com/" rel="nofollow noreferrer">dinero.js</a> library that <a href="https://frontstuff.io/how-to-handle-monetary-values-in-javascript" rel="nofollow noreferrer">addresses many of the issues wrt monetary calculations</a>. Haven't used it yet in a production system so can't give an informed opinion on it.

In the interest of creating cross-platform code, I'd like to develop a simple financial application in JavaScript. The calculations required involve compound interest and relatively long decimal numbers. I'd like to know what mistakes to avoid when using JavaScript to do this type of math—if it is possible at all!

Precise Financial Calculation in JavaScript. What Are the Gotchas?

为了创建跨平台代码，我想用JavaScript开发一个简单的金融应用程序。所需的计算涉及复利和相对较长的十进制数字。我想知道在使用JavaScript进行这种类型的数学运算时应该避免哪些错误--如果可能的话！

问在JavaScript中精确的财务计算。Gotchas是什么？
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