When the user clicks on a space on the board, we want one of two things to happen. If the space is occupied by either an X or an O, write a message telling the user that. If it is an empty space, change the contents of the table cell to be a large letter X. We will write a function to do this. It needs to know the id of the table cell it is going to change. This function will be run when the cell is clicked on. We will use the onClick event handler for this. Remember that the id of the cells was made up of the letter 'b' and a number between 0 and 8. The number is the array index (slot number) of the slot in the board array that holds the contents of that board space. So we can get the second character of the cell id and use that to check and set the board array slot. Next we mark the space with a large, red X.