jQuery UI datepicker datepicker is not a function

Question

When I am using the DatePicker, jQuery's UI plugin, in an existing .aspx page I get errors that:

$("#datepicker").datepicker is not a function

However, when I copy and paste the same code that creates and uses the datePicker to an HTML file that's also in the same directory as the aspx page, it works flawlessly. This leads me to assume that there are some JS files in the aspx page that's preventing the datePicker or maybe jQuery's UI JS files from loading properly.

Can anyone confirm my beliefs or provide any tips on finding the culprit that's interfering with jQuery's UI plugins?

Answer 1

I struggled with a similar problem for a couple of hours but later, it turned out that jQuery was included twice, once by the program that I was adding a jQuery function to and once by our in-house debugger. Hope this helps you solve the issue which interferes with jQuery's UI plugins.