fix(@toss/validators): Increase the accuracy of verification for isBirthDate6

[po4tion]

Overview

[ What did i do ]
According to the Gregorian calendar, there are months when 30 or 31 days do not exist. For example, February 30 and April 31.
The current "isBirthDate6" is not responsible for this, even though it is a function to verify the correct date of birth. So I've supplemented this.

[ AS-IS ]

[ TO-BE ]

expect(isBirthDate6('950230')).toEqual(false);
expect(isBirthDate6('950431')).toEqual(false);

PR Checklist

• I read and included theses actions below

1. I have read the Contributing Guide
2. I have written documents and tests, if needed.

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[okinawaa]

I think there are too many expect phrases to verify on one test suite(it).
Why don't you split it up in different test suite?

[po4tion]

@okinawaa I agree with you. Changed Code

[ssi02014]

@po4tion 👋 cc. @okinawaa

The leap year check for the year 2000 is currently incorrect. ex) 000229

// as-is Abnormal behavior 
isBirthDate6("000229"); // false
[31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]

// to-be Normal behavior 
isBirthDate6("000229"); // true
[31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]

There are actually 29 days in February 2000.
https://ko.wikipedia.org/wiki/2000%EB%85%84_2%EC%9B%94

Suggested change

	function isLeapYear(year: number) {
	return year !== 0 && year % 4 === 0;
	}
	function isLeapYear(year: number) {
	return year % 4 === 0;
	}

Wouldn't the above code be more accurate!? 🤗

[po4tion]

@ssi02014 Thank you for finding a bug! I apply the code you suggested. Changed Code

[ssi02014]

A small suggestion..!
Why not define the numbers 1 and 12 as JANUARY and DECEMBER constants to manage them? 🤗

Suggested change

	if (month < 1 || month > 12) {
	return false;
	}
	if (month < JANUARY || month > DECEMBER) {
	return false;
	}

[okinawaa]

I like This comment awesome..!

[minsoo-web]

I love it too.
This code prevents the use of magic numbers

[po4tion]

@ssi02014 Thanks! I agree with you. Changed code (cc. @minsoo-web, @okinawaa )

[raon0211]

Hello @po4tion, thanks for your contribution.

In my opinion, the best way to handle this is using the proper date library, since Dates are hard to handle properly. If we were to use date-fns, we might have used:

import { parse, isValid } from 'date-fns';

const parsed = parse(date, "yyMMdd", new Date());
return isValid(parsed);

How about using the proper library instead of implementing the validation logic ourselves?

[raon0211]

Thanks for your awesome work!

[po4tion]

@raon0211 That's an incredible speed. Your addition was helpful, thank you!