OPIEC | Reading the data from OPIEC - an Open Information | Natural Language Processing library

Wow, that looks like a lot of work ! You might want to either simplify or start fresh to solve your problem. (You can always make it more complex later, but if it doesn't work as you need to ,it's best to make easy to tweak/change first).

Unfortunately I won't be able to provide a snippet for every single problem, but I can point a few things that might help you fix your bug:

1. You already has a condition that checks if the falling piece is at the bottom and it works: if (moveFallingPiece(-1,0) == false) {
2. Currently you only have a single piece and when it reaches the bottom you "recycle" it as a new piece (changing it's Tetris piece type and resetting the row to 0): you might want to create an array to store the pieces that have fallen. This way you can choose stop updating the row (stop them from falling), but keep rendering them on screen and also solve the logic of which parts of which piece connect as a continuos last row
3. The code is very tighly coupled. You might want to re-organise your objects so it's easier to handle multiple pieces, each pieces with parts.

(e.g. create a class and instances (objects) , solve any collisions (be it with the bottom of the screen or other pieces) and add multiple objects to the array as collisions are detected to form full rows (gain points) or stack up)

I would suggest doing a 2D version with p5.js first, then simply change the p5.js renderer to WEBGL and swap your rect() calls for box() calls (taking into account they're drawn from centre and using push()/pop() calls to isolate coordinate spaces for each box). (A bit further down the line you might want to look at the MVC pattern and have the rendering/view separate from the data and control logic, allowing you to change from a 2D to 3D Tetris if you want to)