Customized Locale throws exception while formatting

Describe the bug I am trying to convert a time stamp to a required format ‘LT’.

dayjs(1575872723701);

/* Returns this object
{
$D: 19
$H: 12
$L: undefined
$M: 10
$W: 2
$d: Tue Nov 19 2019 12:26:03 GMT+0530 (India Standard Time) {}
$m: 26
$ms: 136
$s: 3
$y: 2019
}
*/

and all the APIs like add, subtract, date works except format.

dayjs(1575872723701).format() 

returns Uncaught TypeError: Cannot read property ‘10’ of undefined

My usage

• I have created a service file with all the plugin initializations of dayJs and importing it into the application

// services/dayjs.js
import dayjs from 'dayjs';
import advancedFormat from 'dayjs/plugin/advancedFormat';
import relativeTime from 'dayjs/plugin/relativeTime';
import localizedFormat from 'dayjs/plugin/localizedFormat'

dayjs.extend(advancedFormat);
dayjs.extend(relativeTime);
dayjs.extend(localizedFormat)

export default dayjs;

// somefile.js
import dayjs from './services/dayjs.js';

...
dayjs(1575872723701).format()  // throws error

• I dont see any issue with other plugins and APIs except format.

• I also set the locale of the /services/dayjs.js based on the locale sent. if not set to the below default config

import dayjs from './services/dayjs.js';

if(...){
const locale = {
      relativeTime: {
        name: 'en',
        future: '%s',
        past: '%s',
        s: function () {
          return 'now';
        },
        m: 'a minute ago',
        mm: '%d minutes ago',
        h: 'an hour',
        hh: '%d hours', // e.g. 2 hours, %d been replaced with 2
        d: 'a day',
        dd: '%d days',
        M: 'a month',
        MM: '%d months',
        y: 'a year',
        yy: '%d years'
      },
      ordinal: (n) => {
        const s = ['th', 'st', 'nd', 'rd']
        const v = n % 100
        return `[${n}${(s[(v - 20) % 10] || s[v] || s[0])}]`
      }
    }

    dayjs.locale(locale)
}

Would this be causing any error ?

Expected behavior Should ideally format to the provided option

Information

• Day.js Version: 1.8.17
• OS: MAC OS 10.15.1
• Browser: Chrome Version 78.0.3904.108 and all major browsers
• Time zone: GMT + 5.30

[iamkun]

May be some easy way like this

dayjs.Ls['en'].weekdays = ['a', 'b','c','d','e','f','g'] // update locale 
dayjs.locale(dayjs.Ls['en'])
console.log(dayjs().format('dddd'))

[SarathSantoshDamaraju]

I took a workd around. But

I faced this while implementing the custom locale.

If I want to extend the en locale just with relativeTime: {} then the error happens i assume custome locale expects to declare weekdays, weekdaysShort and other related keys as mentioned in the below comment. https://github.com/iamkun/dayjs/issues/746#issuecomment-563927090

This API dosent align with moment implementation. ref: https://runkit.com/embed/6abjer62rzj0

Can see err here : https://runkit.com/embed/32yqrafbgp6j