javascript 中字符和ASCII之间的相互转换

function getsouth()
{
       var southIndex1 = "";
            if(lastIndex == "10")
            {
                southIndex1 = lastIndex;
            }
            else
            {
                southIndex1 = parseInt(lastIndex) + 1;
            }
            var southIndex = firstIndex + southIndex1;    //向下
            return southIndex;
}
function getwest()
{
var westIndex1 = "";
            if(firstIndex == "a")
            {
                westIndex1 = firstIndex;
            }
            else
            {
                westIndex1 = String.fromCharCode(firstIndex.charCodeAt()-1);
            }
            var westIndex = westIndex1 + lastIndex;    //向左
            return westIndex;
}