I am new to Typescript and trying to get the date (X) amount of months or days from now, in the newDate format specified below...

When I try to add one month:

var dateObj = new Date();
var month = dateObj.getUTCMonth()   2;
var day = dateObj.getUTCDate();
var year = dateObj.getUTCFullYear();

var newDate = month   "/"   day   "/"   year;

It returns:

13/6/2022

When I try to add 30 days instead:

var dateObj = new Date();
var month = dateObj.getUTCMonth()   1;
var day = dateObj.getUTCDate()   30;
var year = dateObj.getUTCFullYear();

var newDate = month   "/"   day   "/"   year;

It returns this:

12/36/2022

So not only are the month & day incorrect in the example, the year doesn't advance either.

Any ideas?

CodePudding user response：

Without using Moment or any other library you can use setDate() and getDate() functions to manipulate value of dateObj:

// hard-coded date to illustrate automatic handling of year/month change
var dateObj = new Date('2022-12-06');

// add 30 days
dateObj.setDate(dateObj.getDate()   30); // 2023-01-05

var month = dateObj.getUTCMonth()   1;
var day = dateObj.getUTCDate();
var year = dateObj.getUTCFullYear();

var newDate = month   "/"   day   "/"   year;

console.log(newDate)

Notice how it automatically takes care of changing the month and year automatically for you.

CodePudding user response：

Simply set date with setSate() function.

var future = new Date();
future.setDate(future.getDate()   X_DAYS);

CodePudding user response：

As shown in this answer, you can rely on the Date object's ability to accept and handle invalid (out of range) values when adjusting specific components (e.g. day of month) — it will wrap the number and algorithmically determine how to handle the overflow (remainder), applying it to the next component (e.g. month).

e.g. In the details, adding 30 to 6 results in 36 as the new day of month — that's not a valid value for any month in the JS Date object.

If you don't want to rely on that kind of behavior for some reason — maybe you want a conceptual solution that you could apply to another language or date framework that doesn't handle overflow for you — then you can also adjust the numeric date representation manually using a bit of unit conversion math:

TS Playground

const date = new Date(Date.UTC(2022, 11, 6));
console.log(date.toISOString()); // 2022-12-06T00:00:00.000Z

const dayInMs = 1000 * 60 * 60 * 24;
//              ms/s      min/hr
//                    s/min     hr/day

date.setTime(date.getTime()   (30 * dayInMs));
//           ^^^^^^^^^^^^^^    ^^^^^^^^^^^^
//           date in ms        30 days in ms

console.log(date.toISOString()); // 2023-01-05T00:00:00.000Z