test.js

var GRID_WIDTH  = 10
var GRID_HEIGHT = 8

function random_between(start, end){
  Math.round(Math.random() * (end - start)) + start
}

function randomly_select_bead() {
  random_x = random_between(0, GRID_WIDTH)
  random_y = random_between(0, GRID_HEIGHT)
  PS.BeadColor(random_x, random_y, PS.COLOR_BLACK)
  PS.BeadFunction(random_x, random_y, bead_clicked)
}

function bead_clicked(x,y){
  PS.BeadColor(random_x, random_y, PS.COLOR_WHITE)
  PS.BeadFunction(x,y,null)
  randomly_select_bead()
}

PS.Init = function(){
  PS.GridSize(GRID_WIDTH, GRID_HEIGHT)
  randomly_select_bead()
}