JSFiddle - React, Tailwind, and code Playground

JavaScript

const formatCurrency = (amt) => {
  if (!amt && amt !== 0) return '';
  const sign = (Math.abs(amt) === amt ? '' : '-');
  let amtStr = Math.abs(amt).toFixed(2);
  for (let i = amtStr.length - 6; i > 0; i -= 3) {
    amtStr = `${amtStr.substring(0, i)},${amtStr.substring(i, amtStr.length)}`;
  }
  return `${sign}$${amtStr}`;
};

console.log(formatCurrency(123121000));