JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://unpkg.com/dayjs@1.8.5/dayjs.min.js"></script>
<script src="https://unpkg.com/dayjs@1.8.5/plugin/customParseFormat.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.2.1/moment.min.js"></script>

JavaScript

dayjs.extend(dayjs_plugin_customParseFormat);

const date = '2019/04/19';
const invalidFormat = 'DD';
const momentDate = moment(date, invalidFormat).isValid();
const dayjsDate = dayjs(date, invalidFormat).isValid();
console.log(`is ${date} parsed with ${invalidFormat} valid for moment?`, momentDate);
console.log(`is ${date} parsed with ${invalidFormat} valid for dayjs?`, dayjsDate);
console.log(`...and it's parsed as `, dayjs(date, invalidFormat).toDate());