how to play with array of array

Hi, I'm trying to make a inventory for my game, there have 4 bags each bag has 20 slot inside. now I need a array called bagList() that allow to store slotList1(), slotList2, slotList3(), slotList4(). and each slotList array has different item inside. I have been created them like this: static var bagList= new Array(); static var slotList1=new Array(); static var slotList2=new Array(); static var slotList3=new Array(); static var slotList4=new Array(); //add bags bagList[0]=(slotList1); bagList[1]=(slotList2); bagList[2]=(slotList3); bagList[3]=(slotList4); //add items slotList1[2]=("Assets/Items/testing"); slotList1[15]=("Assets/Items/testing"); slotList3[3]=("Assets/Items/testing"); slotList2[8]=("Assets/Items/testing"); slotList4[11]=("Assets/Items/testing"); that's a good start everything is work. but I got many questions when I'm trying to processing with my arrays. **1.how to get the slotList1.length by through bagList? (eg:bagList[1].length)** **2.how to get the first item that inside slotList1 by through bagList? (eg:bagList[1][0])** **3.how to add item to slotList1 by through bagList? (eg:bagList[1][0][2]="apple")** I know how to get/add items for single array (eg:slotList1[2]="apple") but in my game situation that must take bagList first then slotList. can anyone help me please? If you can bring some example that would be perfect! (JavaScript please)