Fix TS compiler errors and pin TS to 2.7

package.json

@@ -38,7 +38,7 @@
     "through2": "^2.0.3",
     "ts-node": "^3.3.0",
     "tslint": "^5.5.0",
-    "typescript": "^2.5.1",
+    "typescript": "~2.7.0",
     "xml2js": "^0.4.19"
   },
   "contributors": [

packages/grpc-js-core/package.json

@@ -19,7 +19,7 @@
     "@types/node": "^8.0.55",
     "clang-format": "^1.0.55",
     "gts": "^0.5.1",
-    "typescript": "^2.6.1"
+    "typescript": "~2.7.0"
   },
   "contributors": [
     {

packages/grpc-js-core/src/channel.ts

@@ -76,7 +76,7 @@ export class Http2Channel extends EventEmitter implements Channel {
   private connectivityState: ConnectivityState = ConnectivityState.IDLE;
   /* For now, we have up to one subchannel, which will exist as long as we are
    * connecting or trying to connect */
-  private subChannel: http2.ClientHttp2Session|null;
+  private subChannel: http2.ClientHttp2Session|null = null;
   private filterStackFactory: FilterStackFactory;
 
   private subChannelConnectCallback: ()=>void = () => {};
@@ -123,7 +123,7 @@ export class Http2Channel extends EventEmitter implements Channel {
   }
 
   // Transition from any of a set of oldStates to a specific newState
-  private transitionToState(oldStates: [ConnectivityState], newState: ConnectivityState): void {
+  private transitionToState(oldStates: ConnectivityState[], newState: ConnectivityState): void {
     if (oldStates.indexOf(this.connectivityState) > -1) {
       let oldState: ConnectivityState = this.connectivityState;
       this.connectivityState = newState;

packages/grpc-js-core/test/test-call-stream.ts

@@ -38,11 +38,11 @@ class ClientHttp2StreamMock extends stream.Duplex implements http2.ClientHttp2St
   }
   bytesRead = 0;
   dataFrame = 0;
-  aborted: boolean;
-  destroyed: boolean;
-  rstCode: number;
-  session: http2.Http2Session;
-  state: http2.StreamState;
+  aborted: boolean = false;
+  destroyed: boolean = false;
+  rstCode: number = 0;
+  session: http2.Http2Session = {} as any;
+  state: http2.StreamState = {} as any;
   priority = mockFunction;
   rstStream = mockFunction;
   rstWithNoError = mockFunction;

packages/grpc-js-core/test/test-channel-credentials.ts

@@ -8,7 +8,7 @@ import {ChannelCredentials} from '../src/channel-credentials';
 import {assert2, mockFunction} from './common';
 
 class CallCredentialsMock implements CallCredentials {
-  child: CallCredentialsMock;
+  child: CallCredentialsMock|null = null;
   constructor(child?: CallCredentialsMock) {
     if (child) {
       this.child = child;

packages/grpc-js/package.json

@@ -29,6 +29,6 @@
   },
   "devDependencies": {
     "gts": "^0.5.1",
-    "typescript": "^2.6.1"
+    "typescript": "~2.7.0"
   }
 }