Javascript how to format numbers iwth commas code example

Example 1: js format number thousands separator

function numberWithCommas(x) {
    return x.toString().replace(/\B(?<!\.\d*)(?=(\d{3})+(?!\d))/g, ",");
}

Example 2: format number with commas js

foramtNumber = (num,div=",")=>{
  return num.toString().replace(/\B(?=(\d{3})+(?!\d))/g, div);

}