addClass = function addClass(id) {
  var classId = splitClassNameAndType(id); // Only add class if not exists

  if (typeof classes[classId.className] !== 'undefined') return;
  classes[classId.className] = {
    id: classId.className,
    type: classId.type,
    cssClasses: [],
    methods: [],
    members: [],
    annotations: [],
    domId: MERMAID_DOM_ID_PREFIX + classId.className + '-' + classCounter
  };
  classCounter++;
}
Function to lookup domId from id in the graph definition.
@param id
@public