Number to text

num2text.ts

class NumberToWords {
  private ones: string[] = [
    'zero', 'one', 'two', 'three', 'four', 'five', 'six', 'seven', 'eight', 'nine',
    'ten', 'eleven', 'twelve', 'thirteen', 'fourteen', 'fifteen', 'sixteen',
    'seventeen', 'eighteen', 'nineteen'
  ];

  private teens: string[] = this.ones.slice(10); // Reuse for teens

  private tens: string[] = [
    '', '', 'twenty', 'thirty', 'forty', 'fifty', 'sixty', 'seventy', 'eighty', 'ninety'
  ];

  private convertWithUnit(value: number, divisor: number, unit: string): string {
    const quotient = Math.floor(value / divisor);
    const remainder = value % divisor;
    let result = this.convert(quotient) + ' ' + unit;
    if (remainder > 0) {
      result += ' ' + this.convert(remainder);
    }
    return result;
  }

  convert(value: number): string {
    if (value === 0) return 'zero';
    if (value < 0) return 'minus ' + this.convert(Math.abs(value));

    switch (true) {
      case value < 10:
        return this.ones[value];

      case value < 20:
        return this.teens[value - 10];

      case value < 100:
        return this.tens[Math.floor(value / 10)] +
          (value % 10 !== 0 ? ' ' + this.ones[value % 10] : '');

      case value < 1e3:
        return this.convertWithUnit(value, 100, 'hundred');

      case value < 1e6:
        return this.convertWithUnit(value, 1e3, 'thousand');

      case value < 1e9:
        return this.convertWithUnit(value, 1e6, 'million');

      case value < 1e12:
        return this.convertWithUnit(value, 1e9, 'billion');

      default:
        return this.convertWithUnit(value, 1e12, 'trillion');
    }
  }

  convertCurrency(value: number): string {
    const dollars = Math.floor(value);
    const cents = Math.round((value - dollars) * 100);

    let result = this.convert(dollars) + ' dollars';
    if (cents > 0) {
      result += ' and ' + this.convert(cents) + ' cents';
    }
    return result;
  }
}


const converter = new NumberToWords();

console.log(converter.convert(1234));                    // "one thousand two hundred thirty four"
console.log(converter.convert(1234567));                 // "one million two hundred thirty four thousand five hundred sixty seven"
console.log(converter.convertCurrency(123.45));          // "one hundred twenty three dollars and forty five cents"