如何将 JavaScript 中的数字除以任意精度（例如小数点后 28 位）

我知道https://floating-point-gui.de/ https://floating-point-gui.de/事实上，有许多库可以帮助处理大数，但令人惊讶的是，我找不到任何可以处理除法运算结果中小数点后 19 位以上的库。

我花了几个小时尝试诸如精确数学 https://www.npmjs.com/package/exact-math, 小数.js https://github.com/MikeMcl/decimal.js, 大数.js https://github.com/MikeMcl/bignumber.js， 和别的。

你会如何处理下面标有⭐的情况？

// https://jestjs.io/docs/getting-started#using-typescript

import exactMath from 'exact-math'; // https://www.npmjs.com/package/exact-math
import { Decimal } from 'decimal.js'; // https://github.com/MikeMcl/decimal.js

const testCases = [
  // The following cases work in exact-math but fail in Decimal.js:
  '9999513263875304671192000009',
  '4513263875304671192000009',
  '530467119.530467119',
  // The following cases fail in both Decimal.js and exact-math:
  '1.1998679030467029262556391239', // ⭐ exact-math rounds these 28 decimal places to 17: "1.1998679030467029263000000000"
];

describe('decimals.js', () => {
  testCases.forEach((testCase) => {
    test(testCase, () => {
      expect(new Decimal(testCase).div(new Decimal(1)).toFixed(28)).toBe(testCase); // Dividing by 1 (very simple!)
    });
  });
});

describe('exact-math', () => {
  testCases.forEach((testCase) => {
    test(testCase, () => {
      expect(exactMath.div(testCase, 1, { returnString: true })).toBe(testCase); // Dividing by 1 (very simple!)
    });
  });
});

上面的一些测试用例没有意义（因为我不应该期望输出等于输入，因为我使用的是.toFixed().

然后真正的答案是建议 https://stackoverflow.com/questions/73832451/how-to-divide-numbers-in-javascript-to-arbitrary-precision-e-g-28-decimal-plac#comment130371861_73832451通过@James：使用maxDecimal选项：https://www.npmjs.com/package/exact-math#the-config-maxdecimal-property-usage https://www.npmjs.com/package/exact-math#the-config-maxdecimal-property-usage Or https://mikemcl.github.io/decimal.js/# precision https://mikemcl.github.io/decimal.js/#precision在decimal.js中。

请参阅下面带有 ⭐ 的行。

import exactMath from 'exact-math'; // https://www.npmjs.com/package/exact-math
import { Decimal } from 'decimal.js'; // https://github.com/MikeMcl/decimal.js

/**
 *
 * @param amount {string}
 * @param decimals {number} e.g. 6 would return 6 decimal places like 0.000000
 * @param locale {string} e.g. 'en-US' or 'de-DE'
 * @returns {string} e.g. 1,000.000000
 */
export function getLocaleStringToDecimals(amount: string, decimals: any, locale?: string): string {
  // Thanks to https://stackoverflow.com/a/68906367/ because https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/toLocaleString and https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt/toLocaleString would not work for huge numbers or numbers with many decimal places.

  const decimalFormat = new Intl.NumberFormat(locale, { minimumFractionDigits: 1, maximumFractionDigits: 1 });
  const decimalFullString = '1.1';
  const decimalFullNumber = Number.parseFloat(decimalFullString);
  const decimalChar = decimalFormat.format(decimalFullNumber).charAt(1); // e.g. '.' or ','
  const fixed = new Decimal(amount).toFixed(decimals);
  const [mainString, decimalString] = fixed.split('.'); // ['321321321321321321', '357' | '998']
  const mainFormat = new Intl.NumberFormat(locale, { minimumFractionDigits: 0 });
  let mainBigInt = BigInt(mainString); // 321321321321321321n
  const mainFinal = mainFormat.format(mainBigInt); // '321.321.321.321.321.321' | '321.321.321.321.321.322'
  const decimalFinal = typeof decimalString !== 'undefined' ? `${decimalChar}${decimalString}` : ''; // '.357' | '.998'
  const amountFinal = `${mainFinal}${decimalFinal}`; // '321.321.321.321.321.321,36' | '321.321.321.321.321.322,00'
  // console.log({
  //   amount,
  //   fixed,
  //   mainString,
  //   decimalString,
  //   'decimalString.length': decimalString ? decimalString.length : undefined,
  //   decimalFormat,
  //   decimalFinal,
  //   mainFormat,
  //   mainBigInt,
  //   mainFinal,
  //   amountFinal,
  // });
  return amountFinal;
}

/**
 *
 * @param amount {string}
 * @param decimals {number} e.g. 6 would return 6 decimal places like 0.000000
 * @param divisorPower {number} e.g. 0 for yocto, 24 for [base], 27 for kilo, etc 
 * @param locale {string} e.g. 'en-US' or 'de-DE'
 * @returns {string} e.g. 1,000.000000
 */
export function round(amount: string, decimals = 0, divisorPower = 0, locale?: string): string {
  if (divisorPower < 0) {
    throw new Error('divisorPower must be >= 0');
  }
  const amountCleaned = amount.replaceAll('_', '');
  const divisor = Math.pow(10, divisorPower);
  const value: string = exactMath.div(amountCleaned, divisor, { returnString: true, maxDecimal: amount.length + decimals }); // ⭐ https://www.npmjs.com/package/exact-math#the-config-maxdecimal-property-usage
  // console.log(`round(${amount}, decimals = ${decimals}, divisorPower = ${divisorPower}) = ${value}`, divisor);
  const localeString = getLocaleStringToDecimals(value, decimals, locale);
  return localeString;
}

我的测试用例现在通过了。谢谢！

附：看https://stackoverflow.com/a/68906367/ https://stackoverflow.com/a/68906367/是什么启发了我的代码。