diff --git a/client-ts/signalr/src/HttpClient.ts b/client-ts/signalr/src/HttpClient.ts
index 2f8e329834..d3996e7e6b 100644
--- a/client-ts/signalr/src/HttpClient.ts
+++ b/client-ts/signalr/src/HttpClient.ts
@@ -8,7 +8,7 @@ export interface HttpRequest {
     method?: string;
     url?: string;
     content?: string | ArrayBuffer;
-    headers?: Map<string, string>;
+    headers?: { [key: string]: string };
     responseType?: XMLHttpRequestResponseType;
     abortSignal?: AbortSignal;
     timeout?: number;
@@ -58,7 +58,8 @@ export class DefaultHttpClient extends HttpClient {
             xhr.setRequestHeader("X-Requested-With", "XMLHttpRequest");
 
             if (request.headers) {
-                request.headers.forEach((value, header) => xhr.setRequestHeader(header, value));
+                Object.keys(request.headers)
+                    .forEach((header) => xhr.setRequestHeader(header, request.headers[header]));
             }
 
             if (request.responseType) {
diff --git a/client-ts/signalr/src/HttpConnection.ts b/client-ts/signalr/src/HttpConnection.ts
index 178d67ecba..974a4bdb08 100644
--- a/client-ts/signalr/src/HttpConnection.ts
+++ b/client-ts/signalr/src/HttpConnection.ts
@@ -83,8 +83,9 @@ export class HttpConnection implements IConnection {
                 let headers;
                 const token = this.options.accessTokenFactory();
                 if (token) {
-                    headers = new Map<string, string>();
-                    headers.set("Authorization", `Bearer ${token}`);
+                    headers = {
+                        ["Authorization"]: `Bearer ${token}`,
+                    };
                 }
 
                 const negotiatePayload = await this.httpClient.post(this.resolveNegotiateUrl(this.baseUrl), {
diff --git a/client-ts/signalr/src/HubConnection.ts b/client-ts/signalr/src/HubConnection.ts
index f6aa33f333..3335b5eade 100644
--- a/client-ts/signalr/src/HubConnection.ts
+++ b/client-ts/signalr/src/HubConnection.ts
@@ -25,8 +25,8 @@ export class HubConnection {
     private readonly connection: IConnection;
     private readonly logger: ILogger;
     private protocol: IHubProtocol;
-    private callbacks: Map<string, (invocationEvent: StreamItemMessage | CompletionMessage, error?: Error) => void>;
-    private methods: Map<string, Array<(...args: any[]) => void>>;
+    private callbacks: { [invocationId: string]: (invocationEvent: StreamItemMessage | CompletionMessage, error?: Error) => void };
+    private methods: { [name: string]: Array<(...args: any[]) => void> };
     private id: number;
     private closedCallbacks: ConnectionClosed[];
     private timeoutHandle: NodeJS.Timer;
@@ -53,8 +53,8 @@ export class HubConnection {
         this.connection.onreceive = (data: any) => this.processIncomingData(data);
         this.connection.onclose = (error?: Error) => this.connectionClosed(error);
 
-        this.callbacks = new Map<string, (invocationEvent: HubMessage, error?: Error) => void>();
-        this.methods = new Map<string, Array<(...args: any[]) => void>>();
+        this.callbacks = {};
+        this.methods = {};
         this.closedCallbacks = [];
         this.id = 0;
     }
@@ -79,10 +79,10 @@ export class HubConnection {
                         break;
                     case MessageType.StreamItem:
                     case MessageType.Completion:
-                        const callback = this.callbacks.get(message.invocationId);
+                        const callback = this.callbacks[message.invocationId];
                         if (callback != null) {
                             if (message.type === MessageType.Completion) {
-                                this.callbacks.delete(message.invocationId);
+                                delete this.callbacks[message.invocationId];
                             }
                             callback(message);
                         }
@@ -174,7 +174,7 @@ export class HubConnection {
     }
 
     private invokeClientMethod(invocationMessage: InvocationMessage) {
-        const methods = this.methods.get(invocationMessage.target.toLowerCase());
+        const methods = this.methods[invocationMessage.target.toLowerCase()];
         if (methods) {
             methods.forEach((m) => m.apply(this, invocationMessage.arguments));
             if (invocationMessage.invocationId) {
@@ -189,10 +189,14 @@ export class HubConnection {
     }
 
     private connectionClosed(error?: Error) {
-        this.callbacks.forEach((callback) => {
-            callback(undefined, error ? error : new Error("Invocation canceled due to connection being closed."));
-        });
-        this.callbacks.clear();
+        const callbacks = this.callbacks;
+        this.callbacks = {};
+
+        Object.keys(callbacks)
+            .forEach((key) => {
+                const callback = callbacks[key];
+                callback(undefined, error ? error : new Error("Invocation canceled due to connection being closed."));
+            });
 
         this.cleanupTimeout();
 
@@ -228,12 +232,12 @@ export class HubConnection {
             const cancelInvocation: CancelInvocationMessage = this.createCancelInvocation(invocationDescriptor.invocationId);
             const cancelMessage: any = this.protocol.writeMessage(cancelInvocation);
 
-            this.callbacks.delete(invocationDescriptor.invocationId);
+            delete this.callbacks[invocationDescriptor.invocationId];
 
             return this.connection.send(cancelMessage);
         });
 
-        this.callbacks.set(invocationDescriptor.invocationId, (invocationEvent: CompletionMessage | StreamItemMessage, error?: Error) => {
+        this.callbacks[invocationDescriptor.invocationId] = (invocationEvent: CompletionMessage | StreamItemMessage, error?: Error) => {
             if (error) {
                 subject.error(error);
                 return;
@@ -248,14 +252,14 @@ export class HubConnection {
             } else {
                 subject.next((invocationEvent.item) as T);
             }
-        });
+        };
 
         const message = this.protocol.writeMessage(invocationDescriptor);
 
         this.connection.send(message)
             .catch((e) => {
                 subject.error(e);
-                this.callbacks.delete(invocationDescriptor.invocationId);
+                delete this.callbacks[invocationDescriptor.invocationId];
             });
 
         return subject;
@@ -273,7 +277,7 @@ export class HubConnection {
         const invocationDescriptor = this.createInvocation(methodName, args, false);
 
         const p = new Promise<any>((resolve, reject) => {
-            this.callbacks.set(invocationDescriptor.invocationId, (invocationEvent: StreamItemMessage | CompletionMessage, error?: Error) => {
+            this.callbacks[invocationDescriptor.invocationId] = (invocationEvent: StreamItemMessage | CompletionMessage, error?: Error) => {
                 if (error) {
                     reject(error);
                     return;
@@ -288,14 +292,14 @@ export class HubConnection {
                 } else {
                     reject(new Error(`Unexpected message type: ${invocationEvent.type}`));
                 }
-            });
+            };
 
             const message = this.protocol.writeMessage(invocationDescriptor);
 
             this.connection.send(message)
                 .catch((e) => {
                     reject(e);
-                    this.callbacks.delete(invocationDescriptor.invocationId);
+                    delete this.callbacks[invocationDescriptor.invocationId];
                 });
         });
 
@@ -308,11 +312,11 @@ export class HubConnection {
         }
 
         methodName = methodName.toLowerCase();
-        if (!this.methods.has(methodName)) {
-            this.methods.set(methodName, []);
+        if (!this.methods[methodName]) {
+            this.methods[methodName] = [];
         }
 
-        this.methods.get(methodName).push(method);
+        this.methods[methodName].push(method);
     }
 
     public off(methodName: string, method: (...args: any[]) => void) {
@@ -321,7 +325,7 @@ export class HubConnection {
         }
 
         methodName = methodName.toLowerCase();
-        const handlers = this.methods.get(methodName);
+        const handlers = this.methods[methodName];
         if (!handlers) {
             return;
         }
@@ -329,7 +333,7 @@ export class HubConnection {
         if (removeIdx !== -1) {
             handlers.splice(removeIdx, 1);
             if (handlers.length === 0) {
-                this.methods.delete(methodName);
+                delete this.methods[methodName];
             }
         }
     }
diff --git a/client-ts/signalr/src/Transports.ts b/client-ts/signalr/src/Transports.ts
index 480196bc81..50f23e30b9 100644
--- a/client-ts/signalr/src/Transports.ts
+++ b/client-ts/signalr/src/Transports.ts
@@ -238,7 +238,7 @@ export class LongPollingTransport implements ITransport {
     private async poll(url: string, transferFormat: TransferFormat): Promise<void> {
         const pollOptions: HttpRequest = {
             abortSignal: this.pollAbort.signal,
-            headers: new Map<string, string>(),
+            headers: {},
             timeout: 90000,
         };
 
@@ -248,7 +248,8 @@ export class LongPollingTransport implements ITransport {
 
         const token = this.accessTokenFactory();
         if (token) {
-            pollOptions.headers.set("Authorization", `Bearer ${token}`);
+            // tslint:disable-next-line:no-string-literal
+            pollOptions.headers["Authorization"] = `Bearer ${token}`;
         }
 
         while (!this.pollAbort.signal.aborted) {
@@ -316,8 +317,9 @@ async function send(httpClient: HttpClient, url: string, accessTokenFactory: ()
     let headers;
     const token = accessTokenFactory();
     if (token) {
-        headers = new Map<string, string>();
-        headers.set("Authorization", `Bearer ${accessTokenFactory()}`);
+        headers = {
+            ["Authorization"]: `Bearer ${accessTokenFactory()}`,
+        };
     }
 
     await httpClient.post(url, {
diff --git a/client-ts/tsconfig-base.json b/client-ts/tsconfig-base.json
index 2122a6c242..78b45efe77 100644
--- a/client-ts/tsconfig-base.json
+++ b/client-ts/tsconfig-base.json
@@ -13,6 +13,6 @@
         "noImplicitAny": true,
         "suppressImplicitAnyIndexErrors": true,
         "noEmitOnError": true,
-        "lib": [ "es2016", "dom" ]
+        "lib": [ "es5", "es2015.promise", "es2015.iterable", "dom" ]
     }
 }