Price format super fast function by @studentIvan (Ivan Maslov)

number-to-price.js

/** [E]UR, [S]EK, [G]PB, [P]LN, [D]KK, NOK, CHF, [U]SD, [CA]D */
const defaultNumberToPriceFn = function numberToPrice(n, c) {
  let smb = c || this.currency;
  if (smb[0] === 'E') { smb = '€'; }
  else if (smb[0] === 'U' || (smb[0] === 'C' && smb[1] === 'A')) { smb = '$'; }
  else if (smb[0] === 'S' || smb[0] === 'D') { smb = 'kr'; }
  else if (smb[0] === 'G') { smb = '£'; }
  else if (smb[0] === 'P') { smb = 'zł'; }
  const nR = Math.round(+(n || 0) * 100) / 100;
  const nStr = nR.toString();
  let r = ''; let x = 0; let d = (nR ^ 0) === nR; let adl = 0;
  for (let i = nStr.length - 1; i >= 0; i--) {
    if (!d) {
      if (nStr[i] === '.') {
        d = true; r = ',' + r;
        continue;
      }
      r = nStr[i] + r;
      adl++;
      continue;
    }
    x++;
    if (x % 4 === 0) {
      x = 1;
      r = nStr[i] + ' ' + r;
      continue;
    }
    r = nStr[i] + r;
  }
  return smb === '$'
    ? `$${ r }${ adl === 1 ? '0' : '' } ${ c || this.currency }`
    : r + (adl === 1 ? '0 ' : ' ') + smb;
};

const northAmericaNumberToPriceFn = function northAmericaNumberToPrice(n, c) {
  const smb = '$';
  const nR = Math.round(+(n || 0) * 100) / 100;
  const nStr = nR.toString();
  let r = ''; let x = 0; let d = (nR ^ 0) === nR; let adl = 0;
  for (let i = nStr.length - 1; i >= 0; i--) {
    if (!d) {
      if (nStr[i] === '.') {
        d = true; r = '.' + r;
        continue;
      }
      r = nStr[i] + r;
      adl++;
      continue;
    }
    x++;
    if (x % 4 === 0) {
      x = 1;
      r = nStr[i] + ',' + r;
      continue;
    }
    r = nStr[i] + r;
  }
  return smb === '$'
    ? `$${ r }${ adl === 1 ? '0' : '' } ${ c || this.currency }`
    : r + (adl === 1 ? '0 ' : ' ') + smb;
};

export { defaultNumberToPriceFn, northAmericaNumberToPriceFn }

number-to-price.spec.js

/* eslint-disable */
import chai, { expect } from 'chai';
const { defaultNumberToPriceFn, northAmericaNumberToPriceFn } = require('./number-to-price');

const itShouldDisplayPriceCorrectly = (price, currency, result) =>
  it(`price ${ price } ${ currency } must be equal to ${ result }`, () => {
    expect(defaultNumberToPriceFn(price, currency)).to.equal(result);
  });

const itShouldDisplayPriceCorrectlyNA = (price, currency, result) =>
  it(`price ${ price } ${ currency } must be equal to ${ result }`, () => {
    expect(northAmericaNumberToPriceFn(price, currency)).to.equal(result);
  });

describe('defaultNumberToPriceFn price format test', () => {
  /** simple domain cases */
  for (let i = 0; i < 2; i+=0.01) {
    itShouldDisplayPriceCorrectly(i, 'SEK', (i.toFixed(2) + ' kr').replace('.', ',').replace(',00', ''));
  }
  itShouldDisplayPriceCorrectly(0, 'EUR', '0 €');
  itShouldDisplayPriceCorrectly(0.5, 'EUR', '0,50 €');
  itShouldDisplayPriceCorrectly(10000, 'SEK', '10 000 kr');
  itShouldDisplayPriceCorrectly(5000, 'SEK', '5 000 kr');
  itShouldDisplayPriceCorrectly(5010.23, 'SEK', '5 010,23 kr');
  itShouldDisplayPriceCorrectly(10000, 'DKK', '10 000 kr');
  itShouldDisplayPriceCorrectly(5000, 'DKK', '5 000 kr');
  itShouldDisplayPriceCorrectly(5010.23, 'DKK', '5 010,23 kr');
  itShouldDisplayPriceCorrectly(5010.23, 'PLN', '5 010,23 zł');
  itShouldDisplayPriceCorrectly(10000, 'EUR', '10 000 €');
  itShouldDisplayPriceCorrectly(10000, 'PLN', '10 000 zł');
  itShouldDisplayPriceCorrectly(10000.99, 'EUR', '10 000,99 €');
  itShouldDisplayPriceCorrectly(10000.999, 'EUR', '10 001 €');
  itShouldDisplayPriceCorrectly(10.50, 'EUR', '10,50 €');
  itShouldDisplayPriceCorrectly(10.50, 'NOK', '10,50 NOK');
  itShouldDisplayPriceCorrectly(100000.00, 'NOK', '100 000 NOK');
  itShouldDisplayPriceCorrectly(100000.52, 'NOK', '100 000,52 NOK');
  itShouldDisplayPriceCorrectly(129.9, 'EUR', '129,90 €');
  itShouldDisplayPriceCorrectly(49.9, 'EUR', '49,90 €');
  itShouldDisplayPriceCorrectly(39.95, 'EUR', '39,95 €');
  itShouldDisplayPriceCorrectly(1299, 'NOK', '1 299 NOK');
  itShouldDisplayPriceCorrectly(499, 'NOK', '499 NOK');
  itShouldDisplayPriceCorrectly(108, 'GBP', '108 £');
  itShouldDisplayPriceCorrectly(59.42, 'GBP', '59,42 £');
  itShouldDisplayPriceCorrectly(59.9, 'GBP', '59,90 £');
  itShouldDisplayPriceCorrectly(538922.9, 'GBP', '538 922,90 £');
  itShouldDisplayPriceCorrectly(140, 'CHF', '140 CHF');
  itShouldDisplayPriceCorrectly(29.9, 'CHF', '29,90 CHF');
  itShouldDisplayPriceCorrectly(142.89, 'CHF', '142,89 CHF');
  itShouldDisplayPriceCorrectly(74.95 + 99.90, 'EUR', '174,85 €');
  itShouldDisplayPriceCorrectly(100, 'USD', '$100 USD');
  itShouldDisplayPriceCorrectly(100, 'CAD', '$100 CAD');
  itShouldDisplayPriceCorrectlyNA(100, 'USD', '$100 USD');
  itShouldDisplayPriceCorrectlyNA(100.50, 'USD', '$100.50 USD');
  itShouldDisplayPriceCorrectlyNA(100000.00, 'USD', '$100,000 USD');
  itShouldDisplayPriceCorrectlyNA(100, 'CAD', '$100 CAD');
  itShouldDisplayPriceCorrectlyNA(100.50, 'CAD', '$100.50 CAD');
  itShouldDisplayPriceCorrectlyNA(100000.00, 'CAD', '$100,000 CAD');
});