Teach me how to remove unused javascript codes from multiple html files

Teach me how to remove unused javascript codes from multiple html files

I need someone who can teach me how to remove unused javascript codes from the HTML. As I am a noob web designer, I often need to use different libraries to do the job. That's why I get many unused js codes. I searched on youtube and in there, I found a way to scan all the HTML files and remove the unused CSS codes using gulp. I was looking for a similar method for javascript. I need the easiest and simplest way. So, if you have any better way than gulp is not mandatory.
I am looking forward to learning from you. For your convenience, let me tell you that I am okay with both TeamViewer and AnyDesk.

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Requirements

Must have proper knowledge about javascript and javascript optimization.

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Skills Required

javascript js html