The other answer is not correct. It mixes 2 different things.
In Javascript date and time are the same objects, there is no time object that has no date and no date without time : their native values are milliseconds counted from January 1 1970 at midnight (which is an integer).
In spreadsheets, dates have a native value of an integer representing the number of days since december 31 1899 and time is a decimal value which is the fraction of a day ( 6 hours = 1/4 of a day for example , 0.25 day).
So when you add DATE+TIME (integer+decimal) in a spreadsheet you get a full date with time .
But this is not the case in JavaScript of course and you cannot (obviously) add milliseconds and decimal values to get a valid result as there are no decimal values in JS dates.
For full details about dates I'd suggest to search the web and have a look at the MDN date page
Concerning your specific issue, you can run a small function like below to force the format in your spreadsheet (although you could make it also manually using the 123 menu)
function myFunction() {
var sh = SpreadsheetApp.getActive().getActiveSheet();
sh.getRange('A2:A').setNumberFormat('MMM/dd/yyyy');
sh.getRange('B2:B').setNumberFormat('hh:mm:ss');
}
and use a third column in your SS to simply add column A and B, you will then get a complete date value (with time, the display format should be automatically right)
If you can't use that simple solution then the combination of date and time will be a bit more complex, have a look at this recent post for some suggestions.
Below is a code that converts all your date and time to JS date objects.
function getFullDates(){
var sh = SpreadsheetApp.getActive().getActiveSheet();
var data = sh.getDataRange().getValues();
data.shift();
for(var n in data){
var time = new Date(data[n][1]);
var date = new Date(data[n][0]);
var hrs = Number(Utilities.formatDate(time,Session.getScriptTimeZone(),'HH'));
var min = Number(Utilities.formatDate(time,Session.getScriptTimeZone(),'mm'));
var sec = Number(Utilities.formatDate(time,Session.getScriptTimeZone(),'ss'));
Logger.log('date = '+Utilities.formatDate(date, Session.getScriptTimeZone() ,'dd-MM-yyyy HH:mm:ss'));
Logger.log('time = '+hrs+':'+min+':'+sec);
var dateAndTime = new Date(date).setHours(hrs,min,sec,0);
Logger.log('full date object = '+Utilities.formatDate(new Date(dateAndTime), Session.getScriptTimeZone() ,'dd-MM-yyyy HH:mm:ss'))
}
}
NOTE : be sure to check your SS TimeZone and script TimeZone as well, it seems that you are in GMT+8 China, I tested with these values.
Note 2 : I had to use a small trick in the code above to get hours/minutes and seconds because the normal getHours(), getMinutes() getSeconds() return wrong results. This is a problem that has already been discussed here but I can't remember exactly when and I didn't find the post reference right now...
I show the code for info only, feel free to test to see the issue ;-).
function getFullDatesBug(){
var sh = SpreadsheetApp.getActive().getActiveSheet();
var data = sh.getDataRange().getValues();
data.shift();
for(var n in data){
var time = new Date(data[n][1]);
var date = new Date(data[n][0]);
var hrs = time.getHours();
var min = time.getMinutes();
var sec = time.getSeconds();
Logger.log('date = '+Utilities.formatDate(date, Session.getScriptTimeZone() ,'dd-MM-yyyy HH:mm:ss'));
Logger.log('time = '+hrs+':'+min+':'+sec);
var dateAndTime = new Date(date).setHours(hrs,min,sec,0);
Logger.log('full date object = '+Utilities.formatDate(new Date(dateAndTime), Session.getScriptTimeZone() ,'dd-MM-yyyy HH:mm:ss'))
}
}
