How to add days to Date?

You can create one with:-

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

var date = new Date();

console.log(date.addDays(5));

This takes care of automatically incrementing the month if necessary. For example:

8/31 + 1 day will become 9/1.

The problem with using setDate directly is that it's a mutator and that sort of thing is best avoided. ECMA saw fit to treat Date as a mutable class rather than an immutable structure.

var today = new Date();
var tomorrow = new Date();
tomorrow.setDate(today.getDate()+1);

Be careful, because this can be tricky. When setting tomorrow, it only works because its current value matches the year and month for today. However, setting to a date number like "32" normally will still work just fine to move it to the next month.

Here is the way that use to add days, months, and years for a particular date in Javascript.

// To add Days
var d = new Date();
d.setDate(d.getDate() + 5);

// To add Months
var m = new Date();
m.setMonth(m.getMonth() + 5);

// To add Years
var y = new Date();
y.setFullYear(y.getFullYear() + 5);

The simplest approach that I have implemented is to use Date() itself. `

const days = 15; 
// Date.now() gives the epoch date value (in milliseconds) of current date 
nextDate = new Date( Date.now() + days * 24 * 60 * 60 * 1000)

`

A solution designed for the pipeline operator:

const addDays = days => date => {
  const result = new Date(date);

  result.setDate(result.getDate() + days);

  return result;
};

Usage:

// Without the pipeline operator...
addDays(7)(new Date());

// And with the pipeline operator...
new Date() |> addDays(7);

If you need more functionality, I suggest looking into the date-fns library.

the simplest answer is, assuming the need is to add 1 day to the current date:

var currentDate = new Date();
var numberOfDayToAdd = 1;
currentDate.setDate(currentDate.getDate() + numberOfDayToAdd );

To explain to you, line by line, what this code does:

1. Create the current date variable named currentDate. By default "new Date()" automatically assigns the current date to the variable.
2. Create a variable to save the number of day(s) to add to the date (you can skip this variable and use directly the value in the third line)
3. Change the value of Date (because Date is the number of the month's day saved in the object) by giving the same value + the number you want. The switch to the next month will be automatic

Without using the second variable, you can replace 7 with your next x days:

let d=new Date(new Date().getTime() + (7 * 24 * 60 * 60 * 1000));

to substract 30 days use (24h=86400000ms)

new Date(+yourDate - 30 *86400000)

var yourDate=new Date();
var d = new Date(+yourDate - 30 *86400000) 

console.log(d)

You can use JavaScript, no jQuery required:

var someDate = new Date();
var numberOfDaysToAdd = 6;
someDate.setDate(someDate.getDate() + numberOfDaysToAdd); 
Formatting to dd/mm/yyyy :

var dd = someDate.getDate();
var mm = someDate.getMonth() + 1;
var y = someDate.getFullYear();

var someFormattedDate = dd + '/'+ mm + '/'+ y;

As simple as this:

new Date((new Date()).getTime() + (60*60*24*1000));

You can try:

var days = 50;

const d = new Date();

d.setDate(d.getDate() + days)

This should work well.

Short:

function addDays(date, number) {
  const newDate = new Date(date);
  return new Date(newDate.setDate(newDate.getDate() + number));
}

console.log({
  tomorrow: addDays(new Date(), 1)
});

Advance:

function addDays(date, number) {
  const newDate = new Date(date);
  return new Date(newDate.setDate(date.getDate() + number));
}

function addMonths(date, number) {
  const newDate = new Date(date);
  return new Date(newDate.setMonth(newDate.getMonth() + number));
}

function addYears(date, number) {
  const newDate = new Date(date);
  return new Date(newDate.setFullYear(newDate.getFullYear() + number));
}

function getNewDate(dateTime) {
  let date = new Date();
  let number = parseInt(dateTime.match(/\d+/)[0]);

  if (dateTime.indexOf('-') != -1)
    number = (-number);

  if (dateTime.indexOf('day') != -1)
    date = addDays(date, number);
  else if (dateTime.indexOf('month') != -1)
    date = addMonths(date, number);
  else if (dateTime.indexOf('year') != -1)
    date = addYears(date, number);

  return date;
}

console.log({
  tomorrow: getNewDate('+1day'),
  yesterday: getNewDate('-1day'),
  nextMonth: getNewDate('+1month'),
  nextYear: getNewDate('+1year'),
});

With fix provide by jperl

Why so complicated?

Let's assume you store the number of days to add in a variable called days_to_add.

Then this short one should do it:

calc_date = new Date(Date.now() +(days_to_add * 86400000));

With Date.now() you get the actual unix timestamp as milliseconds and then you add as many milliseconds as you want to add days to. One day is 24h60min60s*1000ms = 86400000 ms or 864E5.

Generic prototype with no variables, it applies on an existing Date value:

Date.prototype.addDays = function (days) {
    return new Date(this.valueOf() + days * 864e5);
}

Extending prototype in javascript may not be a good idea, especially in professional codebases.

What you want to do is extend the native Date class:

class MyCustomDate extends Date {

  addDays(days) {
    const date = new MyCustomDate(this.valueOf());
    date.setDate(date.getDate() + days);
    return date;
  }
  
}

const today = new MyCustomDate();

const nextWeek = today.addDays(7)

console.log(nextWeek)

This way, if one day Javascript implements a native addDays method, you won't break anything.

There is a problem with this kind of functions, I solve it with parseInt()

Date.prototype.addDays = function(dias) {

    var date = new Date(this.valueOf());
    date.setDate(parseInt(date.getDate()) + parseInt(dias));
    return date;
}

Date.prototype.addMonths = function(months) {
    var date = new Date(this.valueOf());
    date.setMonth(parseInt(date.getMonth()) + parseInt(months));
    return date;
}


Date.prototype.addYears = function(years) {
    var date = new Date(this.valueOf());
    date.setFullYear(parseInt(date.getFullYear()) + parseInt(years));
    return date;
}

The easiest way to get this done is using date-fns library.

var addDays = require('date-fns/add_days')
addDays(date, amount)

The documentation is available in this link here. You can also get this done using moment.js. The reference link is here

Hope it helps!

Some implementations to extend Date https://gist.github.com/netstart/c92e09730f3675ba8fb33be48520a86d

/**
 * just import, like
 *
 * import './../shared/utils/date.prototype.extendions.ts';
 */
declare global {
  interface Date {
    addDays(days: number, useThis?: boolean): Date;

    addSeconds(seconds: number): Date;

    addMinutes(minutes: number): Date;

    addHours(hours: number): Date;

    addMonths(months: number): Date;

    isToday(): boolean;

    clone(): Date;

    isAnotherMonth(date: Date): boolean;

    isWeekend(): boolean;

    isSameDate(date: Date): boolean;

    getStringDate(): string;
  }
}

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

Date.prototype.addSeconds = function(seconds: number) {
  let value = this.valueOf();
  value += 1000 * seconds;
  return new Date(value);
};

Date.prototype.addMinutes = function(minutes: number) {
  let value = this.valueOf();
  value += 60000 * minutes;
  return new Date(value);
};

Date.prototype.addHours = function(hours: number) {
  let value = this.valueOf();
  value += 3600000 * hours;
  return new Date(value);
};

Date.prototype.addMonths = function(months: number) {
  const value = new Date(this.valueOf());

  let mo = this.getMonth();
  let yr = this.getYear();

  mo = (mo + months) % 12;
  if (0 > mo) {
    yr += (this.getMonth() + months - mo - 12) / 12;
    mo += 12;
  } else {
    yr += ((this.getMonth() + months - mo) / 12);
  }

  value.setMonth(mo);
  value.setFullYear(yr);
  return value;
};

Date.prototype.isToday = function(): boolean {
  const today = new Date();
  return this.isSameDate(today);
};

Date.prototype.clone = function(): Date {
  return new Date(+this);
};

Date.prototype.isAnotherMonth = function(date: Date): boolean {
  return date && this.getMonth() !== date.getMonth();
};

Date.prototype.isWeekend = function(): boolean {
  return this.getDay() === 0 || this.getDay() === 6;
};

Date.prototype.isSameDate = function(date: Date): boolean {
  return date && this.getFullYear() === date.getFullYear() && this.getMonth() === date.getMonth() && this.getDate() === date.getDate();
};

Date.prototype.getStringDate = function(): string {
  // Month names in Brazilian Portuguese
  const monthNames = ['Janeiro', 'Fevereiro', 'Março', 'Abril', 'Maio', 'Junho', 'Julho', 'Agosto', 'Setembro', 'Outubro', 'Novembro', 'Dezembro'];
  // Month names in English
  // let monthNames = ['January', 'February', 'March', 'April', 'May', 'June', 'July', 'August', 'September', 'October', 'November', 'December'];
  const today = new Date();
  if (this.getMonth() === today.getMonth() && this.getDay() === today.getDay()) {
    return 'Hoje';
    // return "Today";
  } else if (this.getMonth() === today.getMonth() && this.getDay() === today.getDay() + 1) {
    return 'Amanhã';
    // return "Tomorrow";
  } else if (this.getMonth() === today.getMonth() && this.getDay() === today.getDay() - 1) {
    return 'Ontem';
    // return "Yesterday";
  } else {
    return this.getDay() + ' de ' + this.monthNames[this.getMonth()] + ' de ' + this.getFullYear();
    // return this.monthNames[this.getMonth()] + ' ' + this.getDay() + ', ' +  this.getFullYear();
  }
};


export {};

date d = new Date() // current date

date tomorrow = d.setMonth(d.getMonth(),d.getDate()+1) // return a date incremented by 0 months and 1 day

try this

function addDays(date,days) {        
      var one_day=1000*60*60*24; 
      return new Date(date.getTime()+(days*one_day)).toLocaleDateString(); 
    }

Use js-joda. It is an awesome immutable date and time library for javascript. Here is an excerpt from its cheat-sheet.

Add 17 days to today

LocalDate.now().plusDays(17); 

You can also build the desired date from now multiple operations at once.

LocalDate.now()
  .plusMonths(1)
  .withDayOfMonth(1)
  .minusDays(17); 

Or:

var d = LocalDate.parse('2019-02-23'); 
d.minus(Period.ofMonths(3).plusDays(3)); // '2018-11-20'

My test exemple can do adition an minus in the same instance of Date Object.

Date.prototype.reset = function()
{
    let newDate = new Date(this.timeStamp)
    this.setFullYear        (newDate.getFullYear())
    this.setMonth           (newDate.getMonth())
    this.setDate            (newDate.getDate())
    this.setHours           (newDate.getHours())
    this.setMinutes     (newDate.getMinutes())
    this.setSeconds     (newDate.getSeconds())
    this.setMilliseconds    (newDate.getMilliseconds())
}

Date.prototype.addDays = function(days)
{
      this.timeStamp = this[Symbol.toPrimitive]('number')
      let daysInMiliseconds = (days * (1000 * 60 * 60 * 24))
      this.timeStamp = this.timeStamp + daysInMiliseconds
      this.reset()
}

Date.prototype.minusDays = function(days)
{
      this.timeStamp = this[Symbol.toPrimitive]('number')
      let daysInMiliseconds = (days * (1000 * 60 * 60 * 24))
      if(daysInMiliseconds <= this.timeStamp)
      {
          this.timeStamp = this.timeStamp - daysInMiliseconds
          this.reset()
      }
       
}

var temp = new Date(Date.now())// from now time

console.log(temp.toDateString())
temp.addDays(31)
console.log(temp.toDateString())
temp.minusDays(5)
console.log(temp.toDateString())

I was trying to solve something similar, I prefer the getTime methods but there are some odd time zone based side effects.

ofc replace "today" with whatever date you need and pass the time in also. The key is to get UTC Time and then use milliseconds to do the addition to bypass those side effects.

var now = new Date(Date.now());
var today = new Date(Date.UTC(now.getFullYear(), now.getMonth(), now.getDate()));

const dayInMs = 86400000; //24 hours
const tomorrow = new Date(today.getTime() + dayInMs);    

For everybody who don't know how to make it work : there is a full working code it's not perfect but you can copy past it and it's working.

In InDesign creat a .jsx in the startup scripts folder in "Program Files\Adobe\Adobe InDesign 2021\Scripts\startup scripts".

You can us the Extendscript Toolkit CC in the creative cloud to make it and paste this:

The restart indesign and jjmmyyyy+30 should be in the texte variable. this will show the date like this jj/m/yyyy idk how to make it show 24/07/2021 insted of 24/7/2021 but goodenough for me .

    #targetengine 'usernameVariable'
    function addVariables(openEvent) 
    {  
    var doc = openEvent.parent;  
    while ( doc.constructor.name != "Document" )  
      {  
    if ( doc.constructor.name == "Application" ){ return; }  
        doc = doc.parent;  
      }  
    // from http://stackoverflow.com/questions/563406/add-days-to-datetime


    var someDate = new Date();
    var numberOfDaysToAdd = 30;
    someDate.setDate(someDate.getDate() + numberOfDaysToAdd); 


    var dd = someDate.getDate();
    var mm = someDate.getMonth() + 1;
    var y = someDate.getFullYear();

    var someFormattedDate = dd + '/'+ mm + '/'+ y;  

      createTextVariable(doc, "jjmmyyyy+30", someFormattedDate);  
    }
    function createTextVariable(target, variableName, variableContents)  
    {  
    var usernameVariable = target.textVariables.itemByName(variableName);  
    if (!usernameVariable.isValid)  
      {  
        usernameVariable = target.textVariables.add();  
        usernameVariable.variableType = VariableTypes.CUSTOM_TEXT_TYPE;  
        usernameVariable.name = variableName;  
      }  
      usernameVariable.variableOptions.contents = variableContents;  
    }  
    app.addEventListener('afterOpen', addVariables);