How to add hours to a Date object?

user_111934 0
Viewed 756890

It amazes me that JavaScript's Date object does not implement an add function of any kind.

I simply want a function that can do this:

var now = Date.now();
var fourHoursLater = now.addHours(4);

function Date.prototype.addHours(h) {

   // How do I implement this?

}

I would simply like some pointers in a direction.

  • Do I need to do string parsing?

  • Can I use setTime?

  • How about milliseconds?

Like this:

new Date(milliseconds + 4*3600*1000 /* 4 hours in ms */)?

This seems really hackish though - and does it even work?

datetime javascript
19 Answers

JavaScript itself has terrible Date/Time API's. Nonetheless, you can do this in pure JavaScript:

Date.prototype.addHours = function(h) {
  this.setTime(this.getTime() + (h*60*60*1000));
  return this;
}
user_980480 
Date.prototype.addHours= function(h){
    this.setHours(this.getHours()+h);
    return this;
}

Test:

alert(new Date().addHours(4));
user_808600

Get a date exactly two hours from now, in one line.

You need to pass milliseconds to new Date.

let expiryDate = new Date(new Date().setHours(new Date().getHours() + 2));

        or

let expiryDate2 = new Date(Date.now() + 2 * (60 * 60 * 1000) );


let nowDate = new Date();
let expiryDate = new Date(new Date().setHours(new Date().getHours() + 2));
let expiryDate2 = new Date(Date.now() + 2 * (60 * 60 * 1000) );

console.log('now', nowDate);
console.log('expiry', expiryDate);
console.log('expiry 2', expiryDate2);

user_90315160

If you would like to do it in a more functional way (immutability) I would return a new date object instead of modifying the existing and I wouldn't alter the prototype but create a standalone function. Here is the example:

//JS
function addHoursToDate(date, hours) {
  return new Date(new Date(date).setHours(date.getHours() + hours));
}

//TS
function addHoursToDate(date: Date, hours: number): Date {
  return new Date(new Date(date).setHours(date.getHours() + hours));
}

let myDate = new Date();

console.log(myDate)
console.log(addHoursToDate(myDate,2))

user_74856900
user_610270

This is an easy way to get an incremented or decremented data value.

const date = new Date()
const inc = 1000 * 60 * 60 // an hour
const dec = (1000 * 60 * 60) * -1 // an hour

const _date = new Date(date)
return new Date(_date.getTime() + inc)
return new Date(_date.getTime() + dec)
user_54082740

SPRBRN is correct. In order to account for the beginning/end of the month and year, you need to convert to Epoch and back.

Here's how you do that:

var milliseconds = 0;          //amount of time from current date/time
var sec = 0;                   //(+): future
var min = 0;                   //(-): past
var hours = 2;
var days = 0;

var startDate = new Date();     //start date in local time (we'll use current time as an example)

var time = startDate.getTime(); //convert to milliseconds since epoch

//add time difference
var newTime = time + milliseconds + (1000*sec) + (1000*60*min) + (1000*60*60*hrs) + (1000*60*60*24*days);

var newDate = new Date(newTime); //convert back to date; in this example: 2 hours from right now

Or do it in one line (where variable names are the same as above:

var newDate =
    new Date(startDate.getTime() + millisecond +
        1000 * (sec + 60 * (min + 60 * (hours + 24 * days))));
user_78481280

I think this should do the trick

 var nextHour  = Date.now() + 1000 * 60 * 60;

user_100838660

If you need it as a string, for example:

var defaultTime: new Date().getHours() + 1 + ":" + new Date().getMinutes();
user_47881370

A little messy, but it works!

Given a date format like this: 2019-04-03T15:58

  //Get the start date.
  var start = $("#start_date").val();
  //Split the date and time.
  var startarray = start.split("T");
  var date = startarray[0];
  var time = startarray[1];

  //Split the hours and minutes.
  var timearray = time.split(":");

  var hour = timearray[0];
  var minute = timearray[1];
  //Add an hour to the hour.
  hour++;
  //$("#end_date").val = start;
  $("#end_date").val(""+date+"T"+hour+":"+minute+"");

Your output would be: 2019-04-03T16:58

user_97991080

The easiest way to do it is:

var d = new Date();
d = new Date(d.setHours(d.getHours() + 2));

It will add 2 hours to the current time.

The value of d = Sat Jan 30 2021 23:41:43 GMT+0500 (Pakistan Standard Time).

The value of d after adding 2 hours = Sun Jan 31 2021 01:41:43 GMT+0500 (Pakistan Standard Time).

user_36167310
Related