i18n-js/src/helpers/numberToHuman.ts

A small library to provide I18n on JavaScript.

import { BigNumber } from "bignumber.js";
import sortBy from "lodash/sortBy";
import zipObject from "lodash/zipObject";

import { I18n } from "../I18n";
import { Numeric, NumberToHumanOptions, NumberToHumanUnits } from "../typing";
import { getFullScope } from "./getFullScope";
import { lookup } from "./lookup";
import { roundNumber } from "./roundNumber";
import { inferType } from "./inferType";

/**
 * Set decimal units used to calculate number to human formatting.
 */
const DECIMAL_UNITS = {
  "0": "unit",
  "1": "ten",
  "2": "hundred",
  "3": "thousand",
  "6": "million",
  "9": "billion",
  "12": "trillion",
  "15": "quadrillion",
  "-1": "deci",
  "-2": "centi",
  "-3": "mili",
  "-6": "micro",
  "-9": "nano",
  "-12": "pico",
  "-15": "femto",
};

const INVERTED_DECIMAL_UNITS = zipObject(
  Object.values(DECIMAL_UNITS),
  Object.keys(DECIMAL_UNITS).map((key) => parseInt(key, 10)),
);

/**
 * Pretty prints (formats and approximates) a number in a way it is more
 * readable by humans.
 *
 * @private
 *
 * @param {I18n} i18n The `I18n` instance.
 *
 * @param {Numeric} input The numeric value that will be represented.
 *
 * @param {NumberToHumanOptions} options The formatting options.
 *
 * @return {string} The formatted number.
 */
export function numberToHuman(
  i18n: I18n,
  input: Numeric,
  options: NumberToHumanOptions,
): string {
  const roundOptions = {
    roundMode: options.roundMode,
    precision: options.precision,
    significant: options.significant,
  };

  let units: NumberToHumanUnits;

  if (inferType(options.units) === "string") {
    const scope = options.units as string;
    units = lookup(i18n, scope);

    if (!units) {
      throw new Error(
        `The scope "${i18n.locale}${i18n.defaultSeparator}${getFullScope(
          i18n,
          scope,
          {},
        )}" couldn't be found`,
      );
    }
  } else {
    units = options.units as NumberToHumanUnits;
  }

  let formattedNumber = roundNumber(new BigNumber(input), roundOptions);

  const unitExponents = (units: NumberToHumanUnits) =>
    sortBy(
      Object.keys(units).map((name) => INVERTED_DECIMAL_UNITS[name]),
      (numeric) => numeric * -1,
    );

  const calculateExponent = (num: BigNumber, units: NumberToHumanUnits) => {
    const exponent = num.isZero()
      ? 0
      : Math.floor(Math.log10(num.abs().toNumber()));

    return unitExponents(units).find((exp) => exponent >= exp) || 0;
  };

  const determineUnit = (units: NumberToHumanUnits, exponent: number) => {
    // eslint-disable-next-line @typescript-eslint/ban-ts-comment
    // @ts-ignore
    const expName = DECIMAL_UNITS[exponent.toString()];

    return units[expName] || "";
  };

  const exponent = calculateExponent(new BigNumber(formattedNumber), units);
  const unit = determineUnit(units, exponent);

  formattedNumber = roundNumber(
    new BigNumber(formattedNumber).div(10 ** exponent),
    roundOptions,
  );

  if (options.stripInsignificantZeros) {
    // eslint-disable-next-line prefer-const
    let [whole, significand] = formattedNumber.split(".");
    significand = (significand || "").replace(/0+$/, "");

    formattedNumber = whole;

    if (significand) {
      formattedNumber += `${options.separator}${significand}`;
    }
  }

  return options.format
    .replace("%n", formattedNumber || "0")
    .replace("%u", unit)
    .trim();
}