I am currently working on migrating from momentjs to dayjs.

The part that I’m stuck on is that converting an Dayjs object with ISO8601 under strict mode as momentjs does. At first, I tried to convert the object with CustomParseFormat like below as a documentation described. And it returned invalid date object like below because of issue from a bug in CustomParseFormat.

const dayjs = require('dayjs');
const customParseFormat = require('dayjs/plugin/customParseFormat')
dayjs.extend(customParseFormat);

// not sure that dayjs is utilizing the format in below for ISO8601
const iso8601Format = 'YYYY-MM-DDTHH:mm:ss.sssZ' 
const currentDate = new Date();
console.log(dayjs(currentDate, iso8601Format, true)); 
// the result is like below 
// {
//    '$L': 'en',
//    '$u': undefined,
//    '$d': Invalid Date,
//    '$y': NaN,
//    '$M': NaN,
//    '$D': NaN,
//    '$W': NaN,
//    '$H': NaN,
//    '$m': NaN,
//    '$s': NaN,
//    '$ms': NaN
// }

However, if I converted the object without extending CustomParseFormat, it seems like returning an valid object.

const dayjs = require('dayjs');

// not sure that dayjs is utilizing the format in below for ISO8601
const iso8601Format = 'YYYY-MM-DDTHH:mm:ss.sssZ' 
const currentDate = new Date();
console.log(dayjs(currentDate, iso8601Format, true));
// the result is like below 
// M {
//  '$L': 'en',
//      '$d': 2022-06-10T02:59:43.585Z,
//      '$x': {},
//  '$y': 2022,
//      '$M': 5,
//      '$D': 10,
//      '$W': 5,
//      '$H': 11,
//      '$m': 59,
//      '$s': 43,
//      '$ms': 585
// }

So, my question is that does dayjs allow to parse the date with custom format without using CustomParseFormat? Also, does it guarantee that the result is same as momentjs? Thanks.