usage.js

<script type="text/javascript" src="https://cdn.jsdelivr.net/jquery/latest/jquery.min.js"></script>
<script type="text/javascript" src="https://cdn.jsdelivr.net/momentjs/latest/moment.min.js"></script>
<script type="text/javascript" src="https://cdn.jsdelivr.net/npm/daterangepicker/daterangepicker.min.js"></script>
<link rel="stylesheet" type="text/css" href="https://cdn.jsdelivr.net/npm/daterangepicker/daterangepicker.css" />

@dangrossman I know this is being super picky but there's no need to have type="text/javascript" or type="text/css". Those have been depricated for a while now.

ok

Why didn't you mention Font Awesome here? After all, Font Awesome is needed to display the calendar icon in picker

This library has no calendar icon or any other icons. It does not make use of Font Awesome.

After adding Font Awesome in in page, icon of calendar is appear in datarangepicker input field

There are no input fields in this library. That's your own webpage where you happen to be using the library. That icon was not added by the picker.