Using a Library

If you are doing a lot of date work, you may want to look into JavaScript date libraries like Luxon, Day.js, or Moment.js. For example, with Moment.js, this is simply:

var newDateObj = moment(oldDateObj).add(30, 'm').toDate();

Vanilla Javascript

This is like chaos's answer, but in one line:

var newDateObj = new Date(oldDateObj.getTime() + diff*60000);

Where diff is the difference in minutes you want from oldDateObj's time. It can even be negative.

Or as a reusable function, if you need to do this in multiple places:

function addMinutes(date, minutes) {
    return new Date(date.getTime() + minutes*60000);
}

^{And just in case this is not obvious, the reason we multiply minutes by 60000 is to convert minutes to milliseconds.}

Be Careful with Vanilla Javascript. Dates Are Hard!

You may think you can add 24 hours to a date to get tomorrow's date, right? Wrong!

addMinutes(myDate, 60*24); //DO NOT DO THIS

It turns out, if the user observes daylight saving time, a day is not necessarily 24 hours long. There is one day a year that is only 23 hours long, and one day a year that is 25 hours long. For example, in most of the United States and Canada, 24 hours after midnight, Nov 2, 2014, is still Nov 2:

const NOV = 10; //because JS months are off by one...
addMinutes(new Date(2014, NOV, 2), 60*24); //In USA, prints 11pm on Nov 2, not 12am Nov 3!

This is why using one of the afore-mentioned libraries is a safer bet if you have to do a lot of work with this.

Below is a more generic version of this function that I wrote. I'd still recommend using a library, but that may be overkill/impossible for your project. The syntax is modeled after MySQL DATE_ADD function.

/**
 * Adds time to a date. Modelled after MySQL DATE_ADD function.
 * Example: dateAdd(new Date(), 'minute', 30)  //returns 30 minutes from now.
 * https://stackoverflow.com/a/1214753/18511
 * 
 * @param date  Date to start with
 * @param interval  One of: year, quarter, month, week, day, hour, minute, second
 * @param units  Number of units of the given interval to add.
 */
function dateAdd(date, interval, units) {
  if(!(date instanceof Date))
    return undefined;
  var ret = new Date(date); //don't change original date
  var checkRollover = function() { if(ret.getDate() != date.getDate()) ret.setDate(0);};
  switch(String(interval).toLowerCase()) {
    case 'year'   :  ret.setFullYear(ret.getFullYear() + units); checkRollover();  break;
    case 'quarter':  ret.setMonth(ret.getMonth() + 3*units); checkRollover();  break;
    case 'month'  :  ret.setMonth(ret.getMonth() + units); checkRollover();  break;
    case 'week'   :  ret.setDate(ret.getDate() + 7*units);  break;
    case 'day'    :  ret.setDate(ret.getDate() + units);  break;
    case 'hour'   :  ret.setTime(ret.getTime() + units*3600000);  break;
    case 'minute' :  ret.setTime(ret.getTime() + units*60000);  break;
    case 'second' :  ret.setTime(ret.getTime() + units*1000);  break;
    default       :  ret = undefined;  break;
  }
  return ret;
}

Working jsFiddle demo.

var d1 = new Date (),
    d2 = new Date ( d1 );
d2.setMinutes ( d1.getMinutes() + 30 );
alert ( d2 );

Maybe something like this?

var d = new Date();
var v = new Date();
v.setMinutes(d.getMinutes()+30);

console.log(v)

I always create 7 functions, to work with date in JS:
addSeconds, addMinutes, addHours, addDays, addWeeks, addMonths, addYears.

You can see an example here: http://jsfiddle.net/tiagoajacobi/YHA8x/

How to use:

var now = new Date();
console.log(now.addMinutes(30));
console.log(now.addWeeks(3));

These are the functions:

Date.prototype.addSeconds = function(seconds) {
  this.setSeconds(this.getSeconds() + seconds);
  return this;
};

Date.prototype.addMinutes = function(minutes) {
  this.setMinutes(this.getMinutes() + minutes);
  return this;
};

Date.prototype.addHours = function(hours) {
  this.setHours(this.getHours() + hours);
  return this;
};

Date.prototype.addDays = function(days) {
  this.setDate(this.getDate() + days);
  return this;
};

Date.prototype.addWeeks = function(weeks) {
  this.addDays(weeks*7);
  return this;
};

Date.prototype.addMonths = function (months) {
  var dt = this.getDate();
  this.setMonth(this.getMonth() + months);
  var currDt = this.getDate();
  if (dt !== currDt) {  
    this.addDays(-currDt);
  }
  return this;
};

Date.prototype.addYears = function(years) {
  var dt = this.getDate();
  this.setFullYear(this.getFullYear() + years);
  var currDt = this.getDate();
  if (dt !== currDt) {  
    this.addDays(-currDt);
  }
  return this;
};

One line code

  var afterSomeMinutes = new Date(new Date().getTime() + minutes * 60000);

where minutes is a number

Stop using Moment.js

As recommended by other great answers, in most cases it's best to use a library when dealing dates. However, it's important to know that as of September 2020 Moment.js is considered legacy and should no longer be used in new projects.

Quoting Moment's statement in their official docs:

We would like to discourage Moment from being used in new projects going forward. [...] We now generally consider Moment to be a legacy project in maintenance mode. It is not dead, but it is indeed done.

Modern libraries

Below are alternatives recommended by Moment.

Luxon

Luxon can be thought of as the evolution of Moment. It is authored by Isaac Cambron, a long-time contributor to Moment. Please read Why does Luxon exist? and the For Moment users pages in the Luxon documentation.

• Locales: Intl provided
• Time Zones: Intl provided

import {DateTime} from 'luxon'

function addMinutes(date, minutes) {
    return DateTime.fromJSDate(date).plus({minutes}).toJSDate()
}

Day.js

Day.js is designed to be a minimalist replacement for Moment.js, using a similar API. It is not a drop-in replacement, but if you are used to using Moment's API and want to get moving quickly, consider using Day.js.

• Locales: Custom data files that can be individually imported
• Time Zones: Intl provided, via a plugin

import dayjs from 'dayjs'

function addMinutes(date, minutes) {
    return dayjs(date).add(minutes, 'minutes').toDate()
}

date-fns

Date-fns offers a series of functions for manipulating JavaScript Date objects. For more details, scroll to "Why date-fns?" on the date-fns home page.

• Locales: Custom data files that can be individually imported
• Time Zones: Intl provided, via a separate companion library

import {addMinutes} from 'date-fns'

function addMinutesDemo(date, minutes) {
    return addMinutes(date, minutes)
}

js-Joda

js-Joda is a JavaScript port of Java's Three-Ten Backport, which is the base for JSR-310 implementation of the Java SE 8 java.time package. If you are familiar with java.time, Joda-Time, or Noda Time, you will find js-Joda comparable.

• Locales: Custom data files via add-on module
• Time Zones: Custom data files via add-on module

import {LocalDateTime, nativeJs, convert} from '@js-joda/core'

function addMinutes(date, minutes) {
    return convert(
        LocalDateTime.from(
            nativeJs(date)
        ).plusMinutes(minutes)
    ).toDate()
}

One-liner no utilities:

new Date(+new Date() + 60000*15) // +15 minutes

The easiest way to solve is the to recognize that in javascript dates are just numbers. It starts 0 or 'Wed Dec 31 1969 18:00:00 GMT-0600 (CST). Every 1 represents a millisecond. You can add or subtract milliseconds by getting the value and instantiating a new date using that value. You can manage it pretty easy with that mind.

const minutesToAdjust = 10;
const millisecondsPerMinute = 60000;
const originalDate = new Date('11/20/2017 10:00 AM');
const modifiedDate1 = new Date(originalDate.valueOf() - (minutesToAdjust * millisecondsPerMinute));
const modifiedDate2 = new Date(originalDate.valueOf() + (minutesToAdjust * millisecondsPerMinute));

console.log(originalDate); // Mon Nov 20 2017 10:00:00 GMT-0600 (CST)
console.log(modifiedDate1); // Mon Nov 20 2017 09:50:00 GMT-0600 (CST)
console.log(modifiedDate2); // Mon Nov 20 2017 10:10:00 GMT-0600 (CST)

This is what I do which seems to work quite well:

Date.prototype.addMinutes = function(minutes) {
    var copiedDate = new Date(this.getTime());
    return new Date(copiedDate.getTime() + minutes * 60000);
}

Then you can just call this like this:

var now = new Date();
console.log(now.addMinutes(50));

You should get the value of the current date to get the date with (ms) and add (30 * 60 *1000) to it. Now you have (current date + 30 min) with ms

console.log('with ms', Date.now() + (30 * 60 * 1000))
console.log('new Date', new Date(Date.now() + (30 * 60 * 1000)))

it is simple as it is;

let initial_date = new Date;
let added30Min = new Date(initial_date.getTime() + (30*60*1000));

Here is the ES6 version:

let getTimeAfter30Mins = () => {
  let timeAfter30Mins = new Date();
  timeAfter30Mins = new Date(timeAfter30Mins.setMinutes(timeAfter30Mins.getMinutes() + 30));
};

Call it like:

getTimeAfter30Mins();

Here is my one-liner:

console.log('time: ', new Date(new Date().valueOf() + 60000))

let d = new Date();
d.setMinutes(d.getMinutes() + 30);

// console.log(d)

I feel many of the answers here are lacking a creative component, very much needed for time travel computations. I present my solution for a temporal translation of 30 minutes.

(jsfiddle here)

function fluxCapacitor(n) {
    var delta,sigma=0,beta="ge";
    (function(K,z){

        (function(a,b,c){
            beta=beta+"tT";
            switch(b.shift()) {
                case'3':return z('0',a,c,b.shift(),1);
                case'0':return z('3',a,c,b.pop());
                case'5':return z('2',a,c,b[0],1);
                case'1':return z('4',a,c,b.shift());
                case'2':return z('5',a,c,b.pop());
                case'4':return z('1',a,c,b.pop(),1);
            }
        })(K.pop(),K.pop().split(''),K.pop());
    })(n.toString().split(':'),function(b,a,c,b1,gamma){
       delta=[c,b+b1,a];sigma+=gamma?3600000:0; 
       beta=beta+"im";
    });
    beta=beta+"e";
    return new Date (sigma+(new Date( delta.join(':')))[beta]());
}

You could do this:

let thirtyMinutes = 30 * 60 * 1000; // convert 30 minutes to milliseconds
let date1 = new Date();
let date2 = new Date(date1.getTime() + thirtyMinutes);
console.log(date1);
console.log(date2);

Here is the IsoString version:

console.log(new Date(new Date().setMinutes(new Date().getMinutes() - (30))).toISOString());

var add_minutes =  function (dt, minutes) {
return new Date(dt.getTime() + minutes*60000);
}
 console.log(add_minutes(new Date(2014,10,2), 30).toString());

One way to 'add' 30 minutes is to create a second date object (mostly for demonstration) and set the minutes to minutes + 30. This will account for adjusting the hour as well if the first time is less than 30 minutes from the next hour. (i.e., 4:45 to 5:15)

const first = new Date();
console.log("first date :", first.toString());
const second = new Date(first);
const newMinutes = second.getMinutes() + 30;
console.log("new minutes:", newMinutes);
second.setMinutes(newMinutes);
console.log("second date:", second.toString());

I know that the topic is way too old. But I am pretty sure that there are some developpers who still need this, so I made this simple script for you. I hope you enjoy it!

Hello back, It's 2020 and I've added some modification hope it will help a lot better now!

Hello again, It is 2022 and I came back again to fix some issues and give a better naming for the methods & functions.

function addTimeToDate(addedTime, date){
  let generatedTime = date.getTime();
  if(addedTime.seconds) generatedTime += 1000 * addedTime.seconds; //check for additional seconds 
  if(addedTime.minutes) generatedTime += 1000* 60 * addedTime.minutes;//check for additional minutes 
  if(addedTime.hours) generatedTime += 1000 * 60 * 60 * addedTime.hours;//check for additional hours 
  return new Date(generatedTime);
}

Date.prototype.addTime = function(addedTime){
  return addTimeToDate(addedTime, this);
}

let futureDate = new Date().addTime({
    hours: 16, //Adding one hour
    minutes: 45, //Adding fourty five minutes
    seconds: 0 //Adding 0 seconds return to not adding any second so  we can remove it.
});

<button onclick="console.log(futureDate)">Travel to the future</button>

Use an existing library known to handle the quirks involved in dealing with time calculations. My current favorite is moment.js.

<script src="//cdnjs.cloudflare.com/ajax/libs/moment.js/2.13.0/moment.js"></script>
<script>
 var now = moment(); // get "now"
 console.log(now.toDate()); // show original date
 var thirty = moment(now).add(30,"minutes"); // clone "now" object and add 30 minutes, taking into account weirdness like crossing DST boundries or leap-days, -minutes, -seconds.
 console.log(thirty.toDate()); // show new date
</script>

Other solution:

var dateAv = new Date();
var endTime = new Date(dateAv.getFullYear(), dateAv.getMonth(), dateAv.getDate(), dateAv.getHours(), dateAv.getMinutes() + 30);
          

For the lazy like myself:

Kip's answer (from above) in coffeescript, using an "enum", and operating on the same object:

Date.UNIT =
  YEAR: 0
  QUARTER: 1
  MONTH: 2
  WEEK: 3
  DAY: 4
  HOUR: 5
  MINUTE: 6
  SECOND: 7
Date::add = (unit, quantity) ->
  switch unit
    when Date.UNIT.YEAR then @setFullYear(@getFullYear() + quantity)
    when Date.UNIT.QUARTER then @setMonth(@getMonth() + (3 * quantity))
    when Date.UNIT.MONTH then @setMonth(@getMonth() + quantity)
    when Date.UNIT.WEEK then @setDate(@getDate() + (7 * quantity))
    when Date.UNIT.DAY then @setDate(@getDate() + quantity)
    when Date.UNIT.HOUR then @setTime(@getTime() + (3600000 * quantity))
    when Date.UNIT.MINUTE then @setTime(@getTime() + (60000 * quantity))
    when Date.UNIT.SECOND then @setTime(@getTime() + (1000 * quantity))
    else throw new Error "Unrecognized unit provided"
  @ # for chaining

Just another option, which I wrote:

DP_DateExtensions Library

It's overkill if this is all the date processing that you need, but it will do what you want.

Supports date/time formatting, date math (add/subtract date parts), date compare, date parsing, etc. It's liberally open sourced.

simply you can use this code with momnet library:

console.log(moment(moment()).add(30,"minutes").format('MM/DD/YYYY hh:mm:ss'));

var myDate= new Date();
var MyNewDate = new Date 
(myDate.getFullYear(),myDate.getMonth(),myDate.getDate(),myDate.getMinutes()+10,01,01)

const MINUTE = 60 * 1000;
new Date(Date.parse(yourDate) + numOfMins * MINUTE)