change instanceof

Author: tinayuangao

src/cdk/tree/tree.ts

@@ -123,8 +123,8 @@ export class CdkTree<T> implements CollectionViewer, OnInit, OnDestroy {
     this._onDestroy.next();
     this._onDestroy.complete();
 
-    if (this.dataSource instanceof DataSource) {
-      this.dataSource.disconnect(this);
+    if (this._dataSource && typeof (this._dataSource as DataSource<T>).disconnect === 'function') {
+      (this.dataSource as DataSource<T>).disconnect(this);
     }
 
     if (this._dataSubscription) {
@@ -157,8 +157,8 @@ export class CdkTree<T> implements CollectionViewer, OnInit, OnDestroy {
   private _switchDataSource(dataSource: DataSource<T> | Observable<T[]> | T[]) {
     this._data = new Array<T>();
 
-    if (this.dataSource instanceof DataSource) {
-      this.dataSource.disconnect(this);
+    if (this._dataSource && typeof (this._dataSource as DataSource<T>).disconnect === 'function') {
+      (this.dataSource as DataSource<T>).disconnect(this);
     }
 
     if (this._dataSubscription) {
@@ -183,7 +183,7 @@ export class CdkTree<T> implements CollectionViewer, OnInit, OnDestroy {
 
     // Cannot use `instanceof DataSource` since the data source could be a literal with
     // `connect` function and may not extends DataSource.
-    if ((this._dataSource as DataSource<T>).connect instanceof Function) {
+    if (typeof (this._dataSource as DataSource<T>).connect === 'function') {
       dataStream = (this._dataSource as DataSource<T>).connect(this);
     } else if (this._dataSource instanceof Observable) {
       dataStream = this._dataSource;