diff --git a/src/client/packages/@reactpy/client/package.json b/src/client/packages/@reactpy/client/package.json
index 51b59fed1..ab4bd34ad 100644
--- a/src/client/packages/@reactpy/client/package.json
+++ b/src/client/packages/@reactpy/client/package.json
@@ -6,7 +6,7 @@
   "license": "MIT",
   "name": "@reactpy/client",
   "type": "module",
-  "version": "0.3.0",
+  "version": "0.3.1",
   "dependencies": {
     "event-to-object": "^0.1.2",
     "json-pointer": "^0.6.2"
diff --git a/src/client/packages/@reactpy/client/src/reactpy-client.ts b/src/client/packages/@reactpy/client/src/reactpy-client.ts
index 5b9ad89b1..6f37b55a1 100644
--- a/src/client/packages/@reactpy/client/src/reactpy-client.ts
+++ b/src/client/packages/@reactpy/client/src/reactpy-client.ts
@@ -21,17 +21,17 @@ export interface ReactPyClient {
    *
    * @param message The message to send. Messages must have a `type` property.
    */
-  sendMessage: (message: any) => void;
+  sendMessage(message: any): void;
 
   /**
    * Load a module from the server.
    * @param moduleName The name of the module to load.
    * @returns A promise that resolves to the module.
    */
-  loadModule: (moduleName: string) => Promise<ReactPyModule>;
+  loadModule(moduleName: string): Promise<ReactPyModule>;
 }
 
-export class BaseReactPyClient implements Partial<ReactPyClient> {
+export abstract class BaseReactPyClient implements ReactPyClient {
   private readonly handlers: { [key: string]: ((message: any) => void)[] } = {};
   protected readonly ready: Promise<void>;
   private resolveReady: (value: undefined) => void;
@@ -49,6 +49,9 @@ export class BaseReactPyClient implements Partial<ReactPyClient> {
     };
   }
 
+  abstract sendMessage(message: any): void;
+  abstract loadModule(moduleName: string): Promise<ReactPyModule>;
+
   /**
    * Handle an incoming message.
    *
diff --git a/src/client/tsconfig.package.json b/src/client/tsconfig.package.json
index 02840dc95..9e7fe5f74 100644
--- a/src/client/tsconfig.package.json
+++ b/src/client/tsconfig.package.json
@@ -4,15 +4,18 @@
     "allowSyntheticDefaultImports": true,
     "declaration": true,
     "declarationMap": true,
-    "esModuleInterop": false,
+    "esModuleInterop": true,
     "forceConsistentCasingInFileNames": true,
     "isolatedModules": true,
     "jsx": "react",
     "lib": ["DOM", "DOM.Iterable", "esnext"],
     "module": "esnext",
     "moduleResolution": "node",
+    "noEmitOnError": true,
+    "noUnusedLocals": true,
     "resolveJsonModule": true,
     "skipLibCheck": false,
+    "sourceMap": true,
     "strict": true,
     "target": "esnext"
   }