What could be wrong with Select2?

Question

JavaScript

jQuery.Deferred exception: undefined is not an object (evaluating 'data.slice')

Answer 1

The slice() array method is applied to the data variable, but at this moment data is not an array (it is also an object in the understanding of JS).
Such errors occur when, before processing the array, they forget to register exceptional conditions, when the data object can be formed not as an empty array, but, for example, may contain error information passed from the abstraction layer, which normally generates data as an array .