WordPress includes jQuery with core. Most everyone knows this. But did you also know WordPress includes a great deal of other libraries for your use.
You should take the time to check the documentation on wp_enqueue_script().
But that list actually isn’t complete! For a complete list of registered files inspect `$GLOBALS[‘wp_scripts’]` in the admin UI. Registered scripts might change per requested page. You can also check out the massive amounts of files in wp-includes to see even more.
My point, though, is that 90% of the time, you don’t need ‘your own’ version of something. We have it.
Even datepicker folks (jquery-ui-datepicker).
Check if core works. If you call it right, most of the time it will.