Using a date picker to get date and a time picker I get two variables, this is how I put them together in unixtime format and then pull them out...
let datetime = oDdate+' '+oDtime;
let unixtime = Date.parse(datetime)/1000;
console.log('unixtime:',unixtime);
to prove it:
let milliseconds = unixtime * 1000;
dateObject = new Date(milliseconds);
console.log('dateObject:',dateObject);
enjoy!