event-delegation

document.getElementById("myTable").addEventListener("click",function(e) {
  // e.target was the clicked element
  if(e.target && e.target.nodeName == "td") {
    // Get the CSS classes
    var classes = e.target.className.split(" ");
    // Search for the CSS class!
    if(classes) {
      // For every CSS class the element has...
      for(var x = 0; x < classes.length; x++) {
        // If it has the CSS class we want...
        if(classes[x] == "classA") {
          // Bingo!
        }
      }
    }
  }
});