////////////// Example element
<td id='0-1' class='line' onclick='playerMove(this);' playerName='none'></td>


// Javascript
var currentPlayer = 'red'

function playerMove(element){
    if (element.playerName == 'none'){
        element.playerName = currentPlayer;
        element.style.backgroundColor=currentPlayer;
        if (currentPlayer == 'red'){
            currentPlayer = 'blue';
        } else {
            currentPlayer = 'red';
        }
    }
    displaySelected(element);
    return;
}

function displaySelected(element){
    document.getElementById("selected").innerHTML = element.playerName;
    return;
}