Indicates if there is a previous item.
Returns true if the current item is not the first item in the dataset.
Returns false if the current item is the first item in the dataset.
Calling hasPrevious() on a write-only dataset causes an error.
Note:
A dataset needs to load its data before you call its hasPrevious() function.
Usually a dataset finishes loading a short time after the page it is on finishes
loading. So if you call hasPrevious() inside the page’s onReady()
event handler, the dataset might not be ready yet.
To call hasPrevious() as soon as possible after a page loads, use the dataset's
onReady() function inside the page’s onReady()
event handler to ensure that both the page and the dataset have finished loading.