The codes below return current UTC datetime in string format.
But i am looking for a function in javascript that return current utc datetime in datetime format.
It seems there is no such that function in javascript.
var dateTime_now = new Date();
var dateTime_now_utc_str = dateTime_now.toUTCString();
alert(dateTime_now_utc_str);You already have the Javascript internal DateTime format in the variable dateTime_now. So I think you do want a string output, but not the string Sun, 05 Dec 2021 06:11:15 GMT, because it contains useless strings like Sun and useful, but non-numerical strings like Dec. I am guessing you do want a string output, but containing digits and separators and no words.
var dateTime_now = new Date();
var dateTime_now_utc_str = dateTime_now.toISOString();
console.log(dateTime_now_utc_str);
// Result: 2021-12-05T06:10:54.299ZA detailed explanation of why is given here, by me:
https://stackoverflow.com/a/58347604/7549483
In short, UTC simply means "in the timezone of GMT+0", while ISO is the name of the format yyyy-mm-dd etc. The full name of the date format is ISO 8601.