import { diff } from 'bpmn-js-differ';
var oldDefinitions, newDefinitions; // read with bpmn-moddle
var changes = diff(oldDefinitions, newDefinitions);

console.log(changes._changed);
// {
//   ServiceTask_1: {
//     model: { $type: 'bpmn:ServiceTask', id: 'ServiceTask_1', ... },
//     attrs: { name: { oldValue: '', newValue: 'T' } }
//   }
// }
console.log(changes._removed);
// {
//   SequenceFlow_1: { $type: 'bpmn:SequenceFlow', id: 'SequenceFlow_1' }
// }
console.log(changes._layoutChanged);
// {
//   StartEvent_1: { $type: 'bpmn:StartEvent', id: 'StartEvent_1' }
// }
console.log(changes._added);
// {
//   Participant_1: { $type: 'bpmn:Participant', id: 'Participant_1' }
// }

import BpmnModdle from 'bpmn-moddle';
async function loadModel(diagramXML) {
  const bpmnModdle = new BpmnModdle();
  const { rootElement: definitionsA } = await bpmnModdle.fromXML(diagramXML),
  return rootElement;
}
const definitionsA = await loadModel(aXML);
// ...
// go ahead and use the model