demo issue

[dodomui]

ngOnChanges(changes: SimpleChanges): void { const src = changes['src']; if (src) { this.source = Observable.fromPromise(this.cache.get({src: src.currentValue})).map(v => v.value); } }

While using the demo in my ionic code, receive below error, could you kindly help? Property 'fromPromise' does not exist on type 'typeof Observable'