books/utils/numberFormat.js

const numberFormats = {
  '#,###.##': { fractionSep: '.', groupSep: ',', precision: 2 },
  '#.###,##': { fractionSep: ',', groupSep: '.', precision: 2 },
  '# ###.##': { fractionSep: '.', groupSep: ' ', precision: 2 },
  '# ###,##': { fractionSep: ',', groupSep: ' ', precision: 2 },
  "#'###.##": { fractionSep: '.', groupSep: "'", precision: 2 },
  '#, ###.##': { fractionSep: '.', groupSep: ', ', precision: 2 },
  '#,##,###.##': { fractionSep: '.', groupSep: ',', precision: 2 },
  '#,###.###': { fractionSep: '.', groupSep: ',', precision: 3 },
  '#.###': { fractionSep: '', groupSep: '.', precision: 0 },
  '#,###': { fractionSep: '', groupSep: ',', precision: 0 }
};

module.exports = {
  // parse a formatted number string
  // from "4,555,000.34" -> 4555000.34
  parseNumber(number, format = '#,###.##') {
    if (!number) {
      return 0;
    }
    if (typeof number === 'number') {
      return number;
    }
    const info = this.getFormatInfo(format);
    return parseFloat(this.removeSeparator(number, info.groupSep));
  },

  formatNumber(number, format = '#,###.##', precision = null) {
    if (!number) {
      number = 0;
    }
    let info = this.getFormatInfo(format);
    if (precision) {
      info.precision = precision;
    }
    let is_negative = false;

    number = this.parseNumber(number);
    if (number < 0) {
      is_negative = true;
    }
    number = Math.abs(number);
    number = number.toFixed(info.precision);

    var parts = number.split('.');

    // get group position and parts
    var group_position = info.groupSep ? 3 : 0;

    if (group_position) {
      var integer = parts[0];
      var str = '';

      for (var i = integer.length; i >= 0; i--) {
        var l = this.removeSeparator(str, info.groupSep).length;
        if (format == '#,##,###.##' && str.indexOf(',') != -1) {
          // INR
          group_position = 2;
          l += 1;
        }

        str += integer.charAt(i);

        if (l && !((l + 1) % group_position) && i != 0) {
          str += info.groupSep;
        }
      }
      parts[0] = str
        .split('')
        .reverse()
        .join('');
    }
    if (parts[0] + '' == '') {
      parts[0] = '0';
    }

    // join decimal
    parts[1] = parts[1] && info.fractionSep ? info.fractionSep + parts[1] : '';

    // join
    return (is_negative ? '-' : '') + parts[0] + parts[1];
  },

  getFormatInfo(format) {
    let format_info = numberFormats[format];

    if (!format_info) {
      throw new Error(`Unknown number format "${format}"`);
    }

    return format_info;
  },

  round(num, precision) {
    var is_negative = num < 0 ? true : false;
    var d = parseInt(precision || 0);
    var m = Math.pow(10, d);
    var n = +(d ? Math.abs(num) * m : Math.abs(num)).toFixed(8); // Avoid rounding errors
    var i = Math.floor(n),
      f = n - i;
    var r = !precision && f == 0.5 ? (i % 2 == 0 ? i : i + 1) : Math.round(n);
    r = d ? r / m : r;
    return is_negative ? -r : r;
  },

  removeSeparator(text, sep) {
    return text.replace(new RegExp(sep === '.' ? '\\.' : sep, 'g'), '');
  }
};