如何检查节点中是否存在密钥？

Question

这是结构。我有一个主节点，内部是keys。如何检查该节点内部是否存在特定的key？

apiVersion: v1
items:
- apiVersion: networking.istio.io/v1alpha3
  kind: VirtualService
  metadata:
    creationTimestamp: 2018-07-19T14:33:00Z
    generation: 1
    name: bookinfo
    namespace: default
    resourceVersion: "27242"
    selfLink: /apis/networking.istio.io/v1alpha3/namespaces/default/virtualservices/bookinfo
    uid: a3238ced-8b60-11e8-8bbd-080027f49aa7
  spec:
    gateways:
    - bookinfo-gateway
    hosts:
    - '*'
    http:
    - match:
      - uri:
          exact: /productpage
      - uri:
          exact: /login
      - uri:
          exact: /logout
      - uri:
          prefix: /api/v1/products
      route:
      - destination:
          host: productpage
          port:
            number: 9080
- apiVersion: networking.istio.io/v1alpha3
  kind: VirtualService
  metadata:
    creationTimestamp: 2018-07-26T07:25:08Z
    generation: 1
    name: details
    namespace: default
    resourceVersion: "165316"
    selfLink: /apis/networking.istio.io/v1alpha3/namespaces/default/virtualservices/details
    uid: 068c51e2-90a5-11e8-84d8-080027f49aa7
  spec:
    hosts:
    - details
    http:
    - route:
      - destination:
          host: details
          subset: v1
- apiVersion: networking.istio.io/v1alpha3
  kind: VirtualService
  metadata:
    creationTimestamp: 2018-07-26T07:25:08Z
    generation: 1
    name: productpage
    namespace: default
    resourceVersion: "165313"
    selfLink: /apis/networking.istio.io/v1alpha3/namespaces/default/virtualservices/productpage
    uid: 0688fb66-90a5-11e8-84d8-080027f49aa7
  spec:
    gateways:
    - bookinfo
    hosts:
    - productpage
    http:
    - route:
      - destination:
          host: productpage
          subset: v1
- apiVersion: networking.istio.io/v1alpha3
  kind: VirtualService
  metadata:
    creationTimestamp: 2018-07-26T07:25:08Z
    generation: 1
    name: ratings
    namespace: default
    resourceVersion: "165315"
    selfLink: /apis/networking.istio.io/v1alpha3/namespaces/default/virtualservices/ratings
    uid: 068b1107-90a5-11e8-84d8-080027f49aa7
  spec:
    hosts:
    - ratings
    http:
    - route:
      - destination:
          host: ratings
          subset: v1
- apiVersion: networking.istio.io/v1alpha3
  kind: VirtualService
  metadata:
    creationTimestamp: 2018-07-26T07:25:08Z
    generation: 1
    name: reviews
    namespace: default
    resourceVersion: "166771"
    selfLink: /apis/networking.istio.io/v1alpha3/namespaces/default/virtualservices/reviews
    uid: 068a454e-90a5-11e8-84d8-080027f49aa7
  spec:
    hosts:
    - reviews
    http:
    - match:
      - headers:
          cookie:
            regex: ^(.*?;)?(user=mariam)(;.*)?$
      route:
      - destination:
          host: reviews
          subset: v2
    - route:
      - destination:
          host: reviews
          subset: v1
kind: List
metadata:
  resourceVersion: ""
  selfLink: ""

Answer 1

有一个exists函数可以调用。

let ref = firebase.database().ref('yourNode/yourKey');

ref.once("value")
  .then(function(snapshot) {
      console.log(snapshot.exists());  // true
  }