File Manager upload gives error: "Uncaught TypeError: i.indexOf is not a function."

I have defined and overridden a Backend to my File Manager, and defined a simple upload() method along with other methods such as makeFile(), makeDir(), etc. When trying to upload a file from the menu option “Upload file”, it gives the following error:
“Uncaught TypeError: i.indexOf is not a function.”.

I am using the free trial version of webix. I don’t know which update version it is.

Hello @OmarAbdullah,

I have defined and overridden a Backend to my File Manager, and defined a simple upload() method along with other methods such as makeFile(), makeDir(), etc.

Please note that the upload() method of the Backend service simply sets to the upload path of the to-be-processed file (the requested URL and the required server response format are both described in our documentation). The actual upload is handled by the Upload service, which makes use of the inner uploader component located within the File Manager.

Please take a look at the following example of a custom uploader: Code Snippet (note that the uploader override is done in order to maintain compatibility with our current backend, it might not be necessary in your case).

Is there any chance you could provide the code for your overriden Backend service? It is hard to say what the issue is exactly without seeing the code first.