word-number-converter/src/toWords.js

A simple JavaScript library to convert numbers to words and words to numbers. Works in both Node.js and browser environments.

const NUMS_TO_WORDS = {
    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",
};

function numberToWordsBelowThousand(n) {
    let words = [];

    if (n >= 100) {
        words.push(NUMS_TO_WORDS[Math.floor(n / 100)] + " hundred");
        n %= 100;
    }

    if (n > 0) {
        if (n < 20) {
            words.push(NUMS_TO_WORDS[n]);
        } else {
            const tens = Math.floor(n / 10) * 10;
            const units = n % 10;
            words.push(
                NUMS_TO_WORDS[tens] + (units ? "-" + NUMS_TO_WORDS[units] : "")
            );
        }
    }

    return words.join(" ");
}

export function toWords(n) {
    if (n === 0) return "zero";

    let parts = [];
    const THOUSANDS = ["", "thousand", "million"];

    for (let i = 0; n > 0; i++) {
        const chunk = n % 1000;
        if (chunk > 0) {
            const chunkWords = numberToWordsBelowThousand(chunk);
            parts.unshift(chunkWords + (THOUSANDS[i] ? " " + THOUSANDS[i] : ""));
        }
        n = Math.floor(n / 1000);
    }

    return parts.join(" ").trim();
}