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Browser

<script src="path/to/dayjs/dayjs.min.js"></script>
<script>
  dayjs().format()
</script>

CDN resource

Day.js can be included by way of a CDN provider like cdnjs.com, unpkg and jsDelivr ...

<!-- CDN example (jsDelivr) -->
<script src="https://cdn.jsdelivr.net/npm/dayjs@1/dayjs.min.js"></script>
<script>dayjs().format()</script>

Check here for more information about loading locale and plugin.