format-num-util/src/formatNum.js

A utility function to format numbers with currency, unit and millify support.

/**
 * Formats a number with commas, optional currency symbol, unit, and compact/millified format.
 * 
 * @param {Object} options
 * @param {number|string} options.num - Number to format
 * @param {string} [options.unit] - Optional unit like kg, km
 * @param {string} [options.curr] - Optional currency symbol like ₹ or $
 * @param {boolean} [options.millify=false] - Whether to shorten large numbers (e.g. 1K, 1M)
 * @returns {string} Formatted number string
 */
export default function formatNum({ num, unit, curr, millify = false }) {
    if (num === null || num === undefined || num === '') return '-';

    const parsedNumber = parseFloat(num); 
    if (isNaN(parsedNumber)) return '-';

    const isNegative = parsedNumber < 0;
    const absoluteNumber = Math.abs(parsedNumber);

    const millifyNumber = (n) => {
        const suffixes = ['', 'K', 'M', 'B', 'T'];
        if (n < 1000) return n.toString();

        let i = 0;
        let value = n;

        while (value >= 1000 && i < suffixes.length - 1) {
            value /= 1000;
            i++;
        }

        return value.toFixed(1).replace(/\.0$/, '') + suffixes[i];
    };

    const integerPart = parseInt(absoluteNumber.toFixed(2), 10);
    const decimalPart = (absoluteNumber % 1).toFixed(2).slice(2);
    const formattedNumber = integerPart.toLocaleString('en-IN') + (decimalPart !== '00' ? `.${decimalPart}` : '');

    return (
        (isNegative ? '-' : '') +
        (curr ? curr : '') +
        (millify ? millifyNumber(absoluteNumber) : formattedNumber) +
        (unit ? ` ${unit}` : '')
    );
}