Cesium 地图服务器连接不上降级方案

const viewer = new Cesium.Viewer()
const imageryLayers = viewer.imageryLayers;
const provider = new Cesium.SuperMapImageryProvider({
  url: '',
})

Cesium.when(provider.readyPromise,(res) => {
  console.log('provider.readyPromise success', res)
  this.$emit('mapServerConnect', true)
}, (err) => {
  console.error('provider.readyPromise error', err)
  this.$emit('mapServerConnect', false)
})