How can i use a class prototype to make multiple 2-dimensional [self-made] arrays for my tetris pieces?

Question

I am trying to make tetris with javascript and also trying to learn new stuff. this is my first time using ES6 so im kind of stuck atm. My goal is to make a "Pieces" Class that will allow me to pass several instances of multidimensional arrays (ones that i write myself without the use of for loop). Also i just need someone to explain to me exactly what im doing because im just running around in circles.
Heres my code so far:
https://code.sololearn.com/WPRRsswZsAKW/?ref=app
https://code.sololearn.com/WPRRsswZsAKW/?ref=app