[Terribledactyl]

This implementation always moves the nth item, it should only do it most of the time, it could never return the starting array but needs to be able to.

[thethirdone]

This implementation NEVER moves the nth item as that is past the end of the array.

   i = Math.random() * n-- | 0; 

generates a value less than n.

And

    t = array[n];
    array[n] = array[i];
    array[i] = t;

is using a decremented n.

You are being confused by the `n--` in the random selection.