diff --git a/extensions/typescript/src/features/baseCodeLensProvider.ts b/extensions/typescript/src/features/baseCodeLensProvider.ts
index 986cb09b8d08cffb4a6eda75c48b9abd5faf816c..dbfd54eb391c39b1fd3ac4e62f5098c663475c67 100644
--- a/extensions/typescript/src/features/baseCodeLensProvider.ts
+++ b/extensions/typescript/src/features/baseCodeLensProvider.ts
@@ -5,7 +5,7 @@
 
 'use strict';
 
-import { CodeLensProvider, CodeLens, CancellationToken, TextDocument, Range, Uri, Position, Event, EventEmitter, workspace, } from 'vscode';
+import { CodeLensProvider, CodeLens, CancellationToken, TextDocument, Range, Uri, Position, Event, EventEmitter, workspace, ProviderResult, } from 'vscode';
 import * as Proto from '../protocol';
 
 import { ITypescriptServiceClient } from '../typescriptService';
@@ -42,14 +42,14 @@ export abstract class TypeScriptBaseCodeLensProvider implements CodeLensProvider
 		}
 	}
 
-	provideCodeLenses(document: TextDocument, token: CancellationToken): Promise<CodeLens[]> {
+	provideCodeLenses(document: TextDocument, token: CancellationToken): ProviderResult<CodeLens[]> {
 		if (!this.enabled) {
-			return Promise.resolve([]);
+			return [];
 		}
 
 		const filepath = this.client.normalizePath(document.uri);
 		if (!filepath) {
-			return Promise.resolve([]);
+			return [];
 		}
 		return this.client.execute('navtree', { file: filepath }, token).then(response => {
 			if (!response) {
@@ -61,6 +61,9 @@ export abstract class TypeScriptBaseCodeLensProvider implements CodeLensProvider
 				tree.childItems.forEach(item => this.walkNavTree(document, item, null, referenceableSpans));
 			}
 			return referenceableSpans.map(span => new ReferencesCodeLens(document.uri, filepath, span));
+		}, (err: any) => {
+			this.client.error(`'navtree' request failed with error.`, err);
+			return [];
 		});
 	}
 
diff --git a/extensions/typescript/src/features/implementationsCodeLensProvider.ts b/extensions/typescript/src/features/implementationsCodeLensProvider.ts
index ad083c2cbe41797c38844f53915a2e398891f0ae..11f9e99da7cec535127824e78c9630456a0c1b9a 100644
--- a/extensions/typescript/src/features/implementationsCodeLensProvider.ts
+++ b/extensions/typescript/src/features/implementationsCodeLensProvider.ts
@@ -5,7 +5,7 @@
 
 'use strict';
 
-import { CodeLens, CancellationToken, TextDocument, Range, Location } from 'vscode';
+import { CodeLens, CancellationToken, TextDocument, Range, Location, ProviderResult } from 'vscode';
 import * as Proto from '../protocol';
 import * as PConst from '../protocol.const';
 
@@ -22,9 +22,9 @@ export default class TypeScriptImplementationsCodeLensProvider extends TypeScrip
 		super(client, 'implementationsCodeLens.enabled');
 	}
 
-	provideCodeLenses(document: TextDocument, token: CancellationToken): Promise<CodeLens[]> {
+	provideCodeLenses(document: TextDocument, token: CancellationToken): ProviderResult<CodeLens[]> {
 		if (!this.client.apiVersion.has220Features()) {
-			return Promise.resolve([]);
+			return [];
 		}
 		return super.provideCodeLenses(document, token);
 	}
diff --git a/extensions/typescript/src/features/referencesCodeLensProvider.ts b/extensions/typescript/src/features/referencesCodeLensProvider.ts
index b5d249d6d45cadc350470dfba37b269aa91d5be7..ffd29559e1c286fef90498d8243acbc6d3099f8d 100644
--- a/extensions/typescript/src/features/referencesCodeLensProvider.ts
+++ b/extensions/typescript/src/features/referencesCodeLensProvider.ts
@@ -5,7 +5,7 @@
 
 'use strict';
 
-import { CodeLens, CancellationToken, TextDocument, Range, Location } from 'vscode';
+import { CodeLens, CancellationToken, TextDocument, Range, Location, ProviderResult } from 'vscode';
 import * as Proto from '../protocol';
 import * as PConst from '../protocol.const';
 
@@ -22,9 +22,9 @@ export default class TypeScriptReferencesCodeLensProvider extends TypeScriptBase
 		super(client, 'referencesCodeLens.enabled');
 	}
 
-	provideCodeLenses(document: TextDocument, token: CancellationToken): Promise<CodeLens[]> {
+	provideCodeLenses(document: TextDocument, token: CancellationToken): ProviderResult<CodeLens[]> {
 		if (!this.client.apiVersion.has206Features()) {
-			return Promise.resolve([]);
+			return [];
 		}
 		return super.provideCodeLenses(document, token);
 	}
diff --git a/extensions/typescript/src/typescriptServiceClient.ts b/extensions/typescript/src/typescriptServiceClient.ts
index f6292a584ca2fb5b7335ac12699b192a0a4d4a7d..68320e063843318d5a0f6ace8a9900abcf66eb5e 100644
--- a/extensions/typescript/src/typescriptServiceClient.ts
+++ b/extensions/typescript/src/typescriptServiceClient.ts
@@ -917,7 +917,8 @@ export default class TypeScriptServiceClient implements ITypescriptServiceClient
 		return Uri.file(filepath);
 	}
 
-	public execute(command: string, args: any, expectsResultOrToken?: boolean | CancellationToken, token?: CancellationToken): Promise<any> {
+	public execute(command: string, args: any, expectsResultOrToken?: boolean | CancellationToken): Promise<any> {
+		let token: CancellationToken | undefined = undefined;
 		let expectsResult = true;
 		if (typeof expectsResultOrToken === 'boolean') {
 			expectsResult = expectsResultOrToken;
@@ -925,13 +926,13 @@ export default class TypeScriptServiceClient implements ITypescriptServiceClient
 			token = expectsResultOrToken;
 		}
 
-		let request: Proto.Request = {
+		const request: Proto.Request = {
 			seq: this.sequenceNumber++,
 			type: 'request',
 			command: command,
 			arguments: args
 		};
-		let requestInfo: RequestItem = {
+		const requestInfo: RequestItem = {
 			request: request,
 			promise: null,
 			callbacks: null