bug: validation of years with arbitrary number of digits with YYYY is not working

[maxkomarychev]

Describe the bug

Validation does not work properly with the strict flag https://day.js.org/docs/en/parse/is-valid

All these dates are considered valid even though the "YYYY" is used and there are dates which have <4 digits in year:

> const dayjs = require('dayjs')
undefined
> dayjs('2022-02-31', 'YYYY-MM-DD', true).isValid();
true
> 
> dayjs('2022-02-31', 'YYYY-MM-DD', true).isValid();
true
> dayjs('202-02-31', 'YYYY-MM-DD', true).isValid();
true
> dayjs('02-02-31', 'YYYY-MM-DD', true).isValid();
true
> dayjs('2-02-31', 'YYYY-MM-DD', true).isValid();
true

Expected behavior
A clear and concise description of what you expected to happen.

"YYYY" must only allow 4-digit years per spec

https://day.js.org/docs/en/parse/string-format

Information

• Day.js Version: 1.11.11
• OS: macos
• Browser: N/A node
• Time zone: CET

[Shiv-hcr]

Unable to replicate this issue in Node.js. The custom format requires the "customParseFormat" plugin - are you testing with this plugin imported too? I've written a quick test in Node:

import dayjs from "dayjs";

const format = "YYYY-MM-DD";
const strictMode = true;
const dates = [
    "2024-05-30", // control - should be true for both tests
    "2022-02-31",
    "202-02-31",
    "02-02-31",
    "2-02-31",
];

console.log("Test without plugin:")
for (const date of dates) {
    console.log(`Date: ${date}. Result: ${dayjs(date, format, strictMode).isValid()}`);
}

console.log("\nTest with plugin:")
import customParseFormat from "dayjs/plugin/customParseFormat.js";
dayjs.extend(customParseFormat);

for (const date of dates) {
    console.log(`Date: ${date}. Result: ${dayjs(date, format, strictMode).isValid()}`);
}

Output:

Test without plugin:
Date: 2024-05-30. Result: true
Date: 2022-02-31. Result: true
Date: 202-02-31. Result: true
Date: 02-02-31. Result: true
Date: 2-02-31. Result: true

Test with plugin:
Date: 2024-05-30. Result: true
Date: 2022-02-31. Result: false
Date: 202-02-31. Result: false
Date: 02-02-31. Result: false
Date: 2-02-31. Result: false