Minesweeper javascript

Hello so i am trying to program minesweeper and I already generated the random bombs but how do i specifically call the td tags that are right next to the bombs so i can change it to 1,2,3, or 4? I'm using javascript only. Here is the code for the bomb generator. Thanks in advance !

function generateBombs()
    {
        var targetTable = document.getElementsByTagName('table')[0],
        used = [],
        bomb = 0,
        x,
        y;

        while (bomb <= 9) 
            {
            y = Math.round(Math.random() * 7);
            x = Math.round(Math.random() * 7);
                if (used.indexOf(y + ':' + x) === -1) 
                {
                    targetTable.getElementsByTagName("tr")[y]
                        .getElementsByTagName('td')[x]
                        .innerHTML = '<img src="sweeperbomb.png" />';
                    used.push(y + ':' + x);
                    bomb++;
                }
            }
    }