[NativeAOT-LLVM] Enable string interop by value

src/libraries/System.Runtime.InteropServices.JavaScript/src/System.Runtime.InteropServices.JavaScript.csproj

@@ -13,6 +13,7 @@
     <GeneratePlatformNotSupportedAssemblyMessage Condition="'$(TargetPlatformIdentifier)' != 'browser'">SR.SystemRuntimeInteropServicesJavaScript_PlatformNotSupported</GeneratePlatformNotSupportedAssemblyMessage>
     <FeatureWasmManagedThreads Condition="'$(TargetPlatformIdentifier)' == 'browser' and '$(WasmEnableThreads)' == 'true'">true</FeatureWasmManagedThreads>
     <WasmEnableJsInteropByValue Condition="'$(TargetPlatformIdentifier)' == 'browser' and '$(WasmEnableJsInteropByValue)' == '' and '$(FeatureWasmManagedThreads)' == 'true'">true</WasmEnableJsInteropByValue>
+    <WasmEnableJsInteropByValue Condition="'$(TargetPlatformIdentifier)' == 'browser' and '$(RuntimeFlavor)' == 'CoreCLR'">true</WasmEnableJsInteropByValue><!-- TODO-LLVM: This is not upstreamable because it makes the build runtime-specific. -->
     <WasmEnableJsInteropByValue Condition="'$(TargetPlatformIdentifier)' == 'browser' and '$(WasmEnableJsInteropByValue)' == ''">false</WasmEnableJsInteropByValue>
     <DefineConstants Condition="'$(FeatureWasmManagedThreads)' == 'true'">$(DefineConstants);FEATURE_WASM_MANAGED_THREADS</DefineConstants>
     <DefineConstants Condition="'$(WasmEnableJsInteropByValue)' == 'true'">$(DefineConstants);ENABLE_JS_INTEROP_BY_VALUE</DefineConstants>

src/mono/browser/browser.proj

@@ -28,6 +28,7 @@
     <WasmEnableSIMD Condition="'$(WasmEnableSIMD)' == ''">true</WasmEnableSIMD>
     <WasmEnableExceptionHandling Condition="'$(WasmEnableExceptionHandling)' == ''">true</WasmEnableExceptionHandling>
     <WasmEnableJsInteropByValue Condition="'$(WasmEnableJsInteropByValue)' == '' and '$(WasmEnableThreads)' == 'true'">true</WasmEnableJsInteropByValue>
+    <WasmEnableJsInteropByValue Condition="'$(RuntimeFlavor)' == 'CoreCLR'">true</WasmEnableJsInteropByValue>
     <WasmEnableJsInteropByValue Condition="'$(WasmEnableJsInteropByValue)' == ''">false</WasmEnableJsInteropByValue>
     <FilterSystemTimeZones Condition="'$(FilterSystemTimeZones)' == ''">false</FilterSystemTimeZones>
     <EmccCmd>emcc</EmccCmd>

src/tests/nativeaot/SmokeTests/DotnetJs/Program.cs

@@ -34,6 +34,14 @@ internal static int Square(int x)
             return result;
         }
 
+        [JSExport]
+        internal static string Concat(string a, string b)
+        {
+            var result = a + b;
+            Console.WriteLine($"Concatenating '{a}' and '{b}' with result '{result}'");
+            return result;
+        }
+
         [JSExport]
         internal static void Throw() => throw new Exception("This is a test exception");
     }

src/tests/nativeaot/SmokeTests/DotnetJs/wwwroot/main.js

@@ -29,5 +29,10 @@ try {
     console.log(`Thrown expected exception: ${e}`);
 }
 
+const concat = exports.DotnetJsApp.Program.Interop.Concat("Aaa", "Bbb");
+if (concat != "AaaBbb") {
+    result = 15;
+}
+
 console.log(`Exit code ${result}`);
 exit(result);