Minor code review changes

Author: oroztocil

src/Components/WebAssembly/JSInterop/src/PublicAPI.Unshipped.txt

@@ -1,3 +1,4 @@
 #nullable enable
+override Microsoft.JSInterop.WebAssembly.WebAssemblyJSRuntime.BeginInvokeJS(long taskId, string! identifier, string? argsJson, Microsoft.JSInterop.JSCallResultType resultType, long targetInstanceId) -> void
 override Microsoft.JSInterop.WebAssembly.WebAssemblyJSRuntime.BeginInvokeJS(Microsoft.JSInterop.Infrastructure.JSInvocationInfo! invocationInfo) -> void
-override Microsoft.JSInterop.WebAssembly.WebAssemblyJSRuntime.InvokeJS(Microsoft.JSInterop.Infrastructure.JSInvocationInfo! invocationInfo) -> string?
+override Microsoft.JSInterop.WebAssembly.WebAssemblyJSRuntime.InvokeJS(Microsoft.JSInterop.Infrastructure.JSInvocationInfo! invocationInfo) -> string!

src/Components/WebAssembly/JSInterop/src/WebAssemblyJSRuntime.cs

@@ -35,11 +35,11 @@ protected override string InvokeJS(string identifier, [StringSyntax(StringSyntax
             ArgsJson = argsJson,
         };
 
-        return InvokeJS(invocationInfo) ?? "";
+        return InvokeJS(invocationInfo);
     }
 
     /// <inheritdoc />
-    protected override string? InvokeJS(JSInvocationInfo invocationInfo)
+    protected override string InvokeJS(JSInvocationInfo invocationInfo)
     {
         var invocationInfoJson = invocationInfo.ToJson();
 

src/JSInterop/Microsoft.JSInterop.JS/src/src/Microsoft.JSInterop.ts

@@ -35,7 +35,7 @@ export module DotNet {
   }
 
   class JSObject {
-      // TODO(oroztocil): Is it correct to cache functions/properties when they can change?
+      // We cache resolved members. Note that this means we can return stale values if the object has been modified since then.
       _cachedMembers: Map<string, ObjectMemberDescriptor>;
 
       // eslint-disable-next-line @typescript-eslint/no-explicit-any
@@ -78,7 +78,8 @@ export module DotNet {
 
           const result =  { parent, name: lastKey } as ObjectMemberDescriptor;
 
-          if (typeof current === "function") {
+          if (current instanceof Function) {
+              // If the member is a function, we bind the parent object as its "this" context.
               result.func = current.bind(parent);
           }
 
@@ -452,15 +453,15 @@ export module DotNet {
           try {
             const valueOrPromise = this.handleJSCall(targetInstanceId, identifier, callType, argsJson);
 
-            // We only listen for a result if the caller wants to be notified about it
+            // We only await the result if the caller wants to be notified about it
             if (asyncHandle) {
-                // On completion, dispatch result back to .NET
                 const result = await valueOrPromise;
                 const serializedResult = stringifyArgs(this, [
                     asyncHandle,
                     true,
                     createJSCallResult(result, resultType)
                 ]);
+                // On success, dispatch result back to .NET
                 this._dotNetCallDispatcher.endInvokeJSFromDotNet(asyncHandle, true, serializedResult);
             }
           } catch(error: any) {
@@ -470,6 +471,7 @@ export module DotNet {
                     false,
                     formatError(error)
                 ]);
+                // On failure, dispatch error back to .NET
                 this._dotNetCallDispatcher.endInvokeJSFromDotNet(asyncHandle, false, serializedError);
             }
           }
@@ -496,15 +498,15 @@ export module DotNet {
       }
 
       handleJSFunctionCall(identifier: string, func: any, args: unknown[]): any {
-          if (typeof func === "function") {
+          if (func instanceof Function) {
               return func(...args);
           } else {
               throw new Error(`The value '${identifier}' is not a function.`);
           }
       }
 
       handleJSNewCall(identifier: string, func: any, args: unknown[]): any {
-          if (typeof func === "function") {
+          if (func instanceof Function) {
               try {
                   // The new expression throws if the function is not constructible (e.g. an arrow function).
                   return new func(...args);

src/JSInterop/Microsoft.JSInterop/src/Infrastructure/JSInvocationInfo.cs

@@ -10,7 +10,7 @@ namespace Microsoft.JSInterop.Infrastructure;
 /// <summary>
 /// Configuration of an interop call from .NET to JavaScript.
 /// </summary>
-public sealed class JSInvocationInfo
+public readonly struct JSInvocationInfo
 {
     /// <summary>
     /// The identifier for the interop call, or zero if no async callback is required.