add_filter.js

function add_commas(args, change) {
  return function(val) {
    var regex = /(\d+)(\d{3})/
    
    val = val.toString()
    
    while(regex.test(val)) {
      val = val.replace(/(\d+)(\d{3})/, '$1,$2')
    }
    
    change(val)
  }
}