why does javascript getMonth count from 0 and getDate count from 1?

This question is purely to satisfy my curiosity.

In the JavaScript Date object, when you call getMonth() it returns the month but it counts from 0.

0 = January
1 = February 
...

But when you call getDate() it starts counting from 1

1 = 1
2 = 2
... 

Why the inconsistency?

Solution 1:

I assume it's because it would be easier to reference in an array of names, i.e.

var months = ["January", "February", "March", "April", "May", "June", "July",
         "August", "September", "October", "November", "December"];

var d = new Date();

var namedMonth = months[d.getMonth()];

If getMonth() returned 1-12, then programmers would have to do d.getMonth()-1 everytime they wanted a fancy named month.

Days of the month don't have specific "names" per se. The getDate() returns 1-(28-31). We usually just refer to them by their number.

The same concept as getMonth() applies for getDay() also, which returns 0-6 based on the day of the week

var days = ["Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"];

var namedDay = days[d.getDay()];

All this returns something like:

console.log("Month: month[" + d.getMonth() + "]: " + namedMonth); 
//Month: month[3]:  April
console.log("Day: days[" + d.getDay() + "]: " + namedDay); 
// Day: days[4] : Thursday 

Solution 2:

Coming a bit late to this, but the correct answer is here:

https://stackoverflow.com/a/41992352/134120

They (the creators of JavaScript) copied the functionality from the corresponding class in Java (which in turn seems to have been copied from C). And so we're propagating the mistakes of the past 🤦‍♂️