Timestamp Microservice 'franzu'

I finished my project and the results seems good, but if someone can tell me something wrong about the thinking-process, method used or something else, I would really appreciate.

ISO-8601 format:

Timestamp format:


The code:

app.get("/api/timestamp/:date_string?", function(req, res){
  let apiDate = req.params.date_string;
// if params === undefined throw new Date

  if(apiDate === undefined){
    let time = new Date();
    res.send({unix: time.getTime(), utc: time.toUTCString()});
//check if there's a dash for the ISO-8601 format 
//and parse the date, else perform a conversion from timestamp

  if(apiDate.indexOf('-') !== -1){
    let parsing = Date.parse(apiDate);
    let utcDate = (new Date(parsing)).toUTCString();
    res.send({unix: parsing, utc: utcDate});
  } else {
    let utcDate = (new Date(+apiDate)).toUTCString();
    res.send({unix: +apiDate, utc: utcDate});

in the last else case why did u add + before apiDate