jQuery UI datepicker datepicker is not a function

Question

When i use 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 to load properly.

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

Answer 1

The "$(...).datepicker is not a function" jQuery error occurs for multiple reasons:

1. Forgetting to include the jQuery UI library.
2. Loading the jQuery UI library before the jQuery library.
3. Loading the jQuery library twice.
4. Specifying an incorrect path to the jQuery files.
5. Using a custom jQuery UI library that does not have a datepicker.