using dyskord.cc/Core
count = 0;
Java.from(mc.thePlayer.inventory.mainInventory).forEach(function (s) {s && s.getItem() instanceof ItemBlock && (count += s.stackSize)});
//converts java array to js array and uses js function
//for (i in mc.thePlayer.inventory.mainInventory) (stack = mc.thePlayer.inventory.mainInventory[i]) && stack.getItem() instanceof ItemBlock && (count += stack.stackSize);
//alternative, cycles through java array via for function
chat.print(count);