convert number to words in javascript [ with explanation]

// Define an object that maps numbers to their word form
const numbersToWords = {
  0: "zero",
  1: "one",
  2: "two",
  3: "three",
  4: "four",
  5: "five",
  6: "six",
  7: "seven",
  8: "eight",
  9: "nine",
  10: "ten",
  11: "eleven",
  12: "twelve",
  13: "thirteen",
  14: "fourteen",
  15: "fifteen",
  16: "sixteen",
  17: "seventeen",
  18: "eighteen",
  19: "nineteen",
  20: "twenty",
  30: "thirty",
  40: "forty",
  50: "fifty",
  60: "sixty",
  70: "seventy",
  80: "eighty",
  90: "ninety",
};

// Define the convertNumberToWords function
function convertNumberToWords(number) {
  // if number present in object no need to go further
  if (number in numbersToWords) return numbersToWords[number];

  // Initialize the words variable to an empty string
  let words = "";

  // If the number is greater than or equal to 100, handle the hundreds place (ie, get the number of hundres)
  if (number >= 100) {
    // Add the word form of the number of hundreds to the words string
    words += convertNumberToWords(Math.floor(number / 100)) + " hundred";

    // Remove the hundreds place from the number
    number %= 100;
  }

  // If the number is greater than zero, handle the remaining digits
  if (number > 0) {
    // If the words string is not empty, add "and"
    if (words !== "") words += " and ";

    // If the number is less than 20, look up the word form in the numbersToWords object
    if (number < 20) words += numbersToWords[number];
    else {
      // Otherwise, add the word form of the tens place to the words string
      //if number = 37, Math.floor(number /10) will give you 3 and 3 * 10 will give you 30
      words += numbersToWords[Math.floor(number / 10) * 10];

      // If the ones place is not zero, add the word form of the ones place
      if (number % 10 > 0) {
        words += "-" + numbersToWords[number % 10];
      }
    }
  }

  // Return the word form of the number
  return words;
}

console.log(convertNumberToWords(123));

Comments

[Pete Oakey]

Add this after let words = "":

if (number >= 1000) {
words += convertNumberToWords(Math.floor(number / 1000)) + " thousand";
number %= 1000;
if (number > 100) words += ', '
}

[Kwesi Aryee]

good one

[Pete Oakey]

You need more test cases.
12345 for example, returns:
"one hundred and twenty-three hundred and forty-five"
Instead, it should return:
"twelve thousand, three hundred and forty-five"