How i can gues the comming value of random array on javascript? [on hold]

I need to know how i can guess the comming random value of array on javascript.

this is an exmple of my code

 const peices = 'ILJOTSZAW';
 matrix = createpeices(peices[peices.length * Math.random() | 0]);

from the array i wanna alert or show de goming value.