如何从Cytoscape生成的JSON中获取所有节点？即我的JSON：{"elements":{"nodes":[{"data":{"id":"pipe2","type":"input","filename":"pipe2"},"position":{"x":100,"y":100},"group":"nodes","removed":false,"selected":false,"selectable":true,"locked":false,"grabbable":true,"classes":""},{"data":{"id":"pipe2sfdfsdf","type":"input",