refractor/pitchslider:fixed linting errors and added js docs

[abhishekkumar08]

Refrences #2767, #2630, #2609

[abhishekkumar08]

@meganindya Have a look.
'_' is assigned a value but never used.
This error is in a loop how to fix this.?

[meganindya]

for (let i = 0; i < this.frequencies.length; i++)

in this case

[abhishekkumar08]

@meganindya please review this.Thanks

[meganindya]

This is fine. But, it would be nice to have a feature. When you're sliding, the value with the hertz block in the widget block doesn't actually change. I think that'd behavior would be better. Please try if you can add that. Shouldn't be difficult.

[abhishekkumar08]

@meganindya I used the frequencey[id] value but coudn't get the desired results, can you tell how should I do this?

[meganindya]

Honestly, I have no idea. Need to look. Anyway, that could be another PR. I'm merging this.