How to create a custom widget based on a standard one?

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So I'm new with creating widgets, and the first thing i'm trying to do is "clone" one so I can then modify it to do slightly different things.

I tried extending the standard widget "ResultsInfo" from reports section, but it doesnt run when trying to use it.

What else do I need to do to make it run/do the same things as the standard widget?

 

PS. I've also tried replacing all the code in the custom to the standard, and it sort of works, but  it has an error message.

"The following widget JavaScript either has a syntax error or its class name is not correct: custom/reports/ResultInfo2"