Add sliding direction

When I use onbeforecallback, I can know the previous step with 'this._currentstep' variable, but I don't know what step I'll have.
Example: I was at step 4, but I don't know if in onbeforecallback I will go at step 3 or 5.
I just add a variable to add this information, -1 for backward and 1 for forward.