The 3rd March 2022 is the end of this Hijri Month (month of Rajab for this year 1443 AH); i.e. 30 Rajab 1443 AH.

The month of Rajab for the year 1443 AH is 30 days in accordance with the Islamic (Hijri) Calendar in accordance with all websites, applications, MS Office, and Windows calendars.

When using the javascript Intl.DateTimeFormat() to display the Islamic (Hijri) date for the 3 March 2022 using the islamic calendar option, it will give the Islamic Hijri Date of (1 Shaʻban 1443 AH). This result is one day after the month of Rajab (i.e. the 1st of the following month) and it calculated the month Rajab to be 29 days rather than 30 days.

However, if the option passed to the Intl.DateTimeFormat() is ar-SA (i.e. arabic-Saudi Arabia), it will give the correct result. This is strange because the ar-SA locale uses the Islamic (Hijri) calendar by default.

Is this an error/bug or is it the correct internal workings of javascript?

Is there a more robust method to get the Islamic Date in Javascript other than using the 'ar-SA' locale (but not using external libraries)?

See the code example below:

I have tested this in node and chrome and it gives the same resulting discrepancy.

let date = new Date("2022-03-03");
let options = {year:'numeric', month:'long',day:'numeric'};

let format = new Intl.DateTimeFormat('ar-SA-u-nu-latn', options);
console.log("3 March 2022 with 'ar-SA'         :"+format.format(date)+ " ==> means: 30 Rajab 1443 AH");

format = new Intl.DateTimeFormat('en-u-ca-islamic-nu-latn', options);
console.log("3 March 2022 with Islamic Calendar: "+format.format(date));