Javascript Date object not showing correct month

Question

I'm trying to use the Javascript Date object to calculate a date in the future (3 months from today). I am however getting unexpected results, specifically, when adding 3 months, the output date is 2025 (for time travelers, it's 2018 this year)!

Doing a simple console.log returns some unexpected results as below:

var d = new Date();
console.log("Locale Time:"+ d.toLocaleDateString());
console.log("Month: "+d.getMonth());
d.setMonth(d.getMonth() + 3);
console.log("3 months from now: "+d.toLocaleDateString());

Returns:
// Note todays real date is 9 October 2018

Locale Time:10/9/2018 // This is correct
app.min.js:1 Month: 9 // No, the month is 10 (October)
app.min.js:1 3 months from now: 11/9/2025 // What?

What am I doing wrong?

https://stackoverflow.com/questions/2552483/why-does-the-month-argument-range-from-0-to-11-in-javascripts-date-constructor — Satpal, Oct 09 '18 at 10:22
I just checked this in my browser (chrome) and had no errors, which console are you using ? — Karan Shishoo, Oct 09 '18 at 10:23
this is very strange as the code is working fine on Edge & Chrome console. I am using Microsoft Edge 42.17134.1.0. and Chrome Version 69.0.3497 Locale Time:10/9/2018 Month: 9 3 months from now: 1/9/2019 — Gaurav joshi, Oct 09 '18 at 10:42
I'm also using Chrome but getting the same results in Firefox. Really not sure what's happening here — mauzilla, Oct 09 '18 at 10:42

score 0 · Answer 1 · answered Oct 09 '18 at 10:29

The argument monthIndex is 0-based. This means that January = 0 and December = 11. so your code can be like this :

var d = new Date();
console.log("Locale Time:"+ d.toLocaleDateString());
console.log("Month: "+d.getMonth());
d.setMonth(d.getMonth() + 4);
console.log("3 months from now: "+d.toLocaleDateString());

Output will be

> "Locale Time:10/9/2018"
> "Month: 9" (October = 9 as monthIndex starts from 0)
> "3 months from now: 2/9/2019"

Javascript Date object not showing correct month

1 Answers1