TypeError: Cannot read property ‘x’ of undefined
This error seems to occur when you are trying to find something out about an undefined list.
The first step is to identify which list is undefined, using Developer Tools. Next, try to work out why it might be undefined at that point in your code. The answer is usually either a blank cell or row in a spreadsheet or the object is being checked too soon.
For example, this code will fail online either in Each Frame or in End Routine if the routine can end without a key press.
numKeys = len(key_resp.keys)
The fix is to confirm that key_resp.keys exists before checking its length:
if key_resp.keys:
numKeys = len(key_resp.keys)