Truncate a given string with plain javascript

truncateString.js

/*
  truncateString
    Truncate a given string
  .parameters
    string (string) - String to truncate
    charNum (integer) - Number of chars to truncate for
    useWordBoundary (boolean) - Use word boundaries, default: false
  .returns
    truncatedString (string) - Truncated string, original string if is below char count
 */
function truncate(string, charNum, useWordBoundary = false) {
  if (string.length <= charNum) return string;
  const filtratedString = string.substr(0, n - 1);
  var truncatedString = useWordBoundary ?
    filtratedString.substr(0, filtratedString.lastIndexOf(" ")) :
    filtratedString + "&hellip;";

  return truncatedString;
}