When you use an `<apex:... id="...">` component, the `id` value gets prefixed. The simplest fix is to use the "ends with" (`$=`) selector:

    var input = $("[id$='notes']");
    var notFound = $("#notes"); // this value is not the literal id

See also:

- [Best Practices for Accessing Component IDs](https://developer.salesforce.com/docs/atlas.en-us.salesforce1api.meta/salesforce1api/pages_best_practices_accessing_id.htm)
- [Using $Component to Reference Components from JavaScript](https://developer.salesforce.com/docs/atlas.en-us.pages.meta/pages/pages_access.htm?search_text=id)
- [$Component](https://developer.salesforce.com/docs/atlas.en-us.pages.meta/pages/pages_variables_global_component.htm?search_text=$component)