diff --git a/teavm-jso-impl/src/main/java/org/teavm/jso/plugin/AstWriter.java b/teavm-jso-impl/src/main/java/org/teavm/jso/impl/AstWriter.java
similarity index 99%
rename from teavm-jso-impl/src/main/java/org/teavm/jso/plugin/AstWriter.java
rename to teavm-jso-impl/src/main/java/org/teavm/jso/impl/AstWriter.java
index 6f53eea8a..7ac5dbbc5 100644
--- a/teavm-jso-impl/src/main/java/org/teavm/jso/plugin/AstWriter.java
+++ b/teavm-jso-impl/src/main/java/org/teavm/jso/impl/AstWriter.java
@@ -13,7 +13,7 @@
  *  See the License for the specific language governing permissions and
  *  limitations under the License.
  */
-package org.teavm.jso.plugin;
+package org.teavm.jso.impl;
 
 import java.io.IOException;
 import java.util.Collections;
diff --git a/teavm-jso-impl/src/main/java/org/teavm/jso/plugin/FunctorImpl.java b/teavm-jso-impl/src/main/java/org/teavm/jso/impl/FunctorImpl.java
similarity index 96%
rename from teavm-jso-impl/src/main/java/org/teavm/jso/plugin/FunctorImpl.java
rename to teavm-jso-impl/src/main/java/org/teavm/jso/impl/FunctorImpl.java
index 198291c0a..6758a71d8 100644
--- a/teavm-jso-impl/src/main/java/org/teavm/jso/plugin/FunctorImpl.java
+++ b/teavm-jso-impl/src/main/java/org/teavm/jso/impl/FunctorImpl.java
@@ -13,7 +13,7 @@
  *  See the License for the specific language governing permissions and
  *  limitations under the License.
  */
-package org.teavm.jso.plugin;
+package org.teavm.jso.impl;
 
 import java.lang.annotation.ElementType;
 import java.lang.annotation.Retention;
diff --git a/teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JS.java b/teavm-jso-impl/src/main/java/org/teavm/jso/impl/JS.java
similarity index 99%
rename from teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JS.java
rename to teavm-jso-impl/src/main/java/org/teavm/jso/impl/JS.java
index 496759487..98d9d97b6 100644
--- a/teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JS.java
+++ b/teavm-jso-impl/src/main/java/org/teavm/jso/impl/JS.java
@@ -13,7 +13,7 @@
  *  See the License for the specific language governing permissions and
  *  limitations under the License.
  */
-package org.teavm.jso.plugin;
+package org.teavm.jso.impl;
 
 import java.lang.reflect.Array;
 import java.util.function.Function;
diff --git a/teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JSOAliasRenderer.java b/teavm-jso-impl/src/main/java/org/teavm/jso/impl/JSAliasRenderer.java
similarity index 93%
rename from teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JSOAliasRenderer.java
rename to teavm-jso-impl/src/main/java/org/teavm/jso/impl/JSAliasRenderer.java
index 9ad375ac9..8a5e7f097 100644
--- a/teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JSOAliasRenderer.java
+++ b/teavm-jso-impl/src/main/java/org/teavm/jso/impl/JSAliasRenderer.java
@@ -13,13 +13,13 @@
  *  See the License for the specific language governing permissions and
  *  limitations under the License.
  */
-package org.teavm.jso.plugin;
+package org.teavm.jso.impl;
 
 import java.io.IOException;
 import java.util.Map;
 import org.teavm.codegen.SourceWriter;
 import org.teavm.javascript.RenderingContext;
-import org.teavm.jso.plugin.JSODependencyListener.ExposedClass;
+import org.teavm.jso.impl.JSDependencyListener.ExposedClass;
 import org.teavm.model.MethodDescriptor;
 import org.teavm.vm.BuildTarget;
 import org.teavm.vm.spi.RendererListener;
@@ -28,12 +28,12 @@ import org.teavm.vm.spi.RendererListener;
  *
  * @author Alexey Andreev
  */
-class JSOAliasRenderer implements RendererListener {
+class JSAliasRenderer implements RendererListener {
     private static String variableChars = "abcdefghijklmnopqrstuvwxyz";
-    private JSODependencyListener dependencyListener;
+    private JSDependencyListener dependencyListener;
     private SourceWriter writer;
 
-    public JSOAliasRenderer(JSODependencyListener dependencyListener) {
+    public JSAliasRenderer(JSDependencyListener dependencyListener) {
         this.dependencyListener = dependencyListener;
     }
 
diff --git a/teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JSBodyAstEmitter.java b/teavm-jso-impl/src/main/java/org/teavm/jso/impl/JSBodyAstEmitter.java
similarity index 98%
rename from teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JSBodyAstEmitter.java
rename to teavm-jso-impl/src/main/java/org/teavm/jso/impl/JSBodyAstEmitter.java
index 0683f027d..29c46d1e8 100644
--- a/teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JSBodyAstEmitter.java
+++ b/teavm-jso-impl/src/main/java/org/teavm/jso/impl/JSBodyAstEmitter.java
@@ -13,7 +13,7 @@
  *  See the License for the specific language governing permissions and
  *  limitations under the License.
  */
-package org.teavm.jso.plugin;
+package org.teavm.jso.impl;
 
 import java.io.IOException;
 import org.mozilla.javascript.ast.AstNode;
diff --git a/teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JSBodyBloatedEmitter.java b/teavm-jso-impl/src/main/java/org/teavm/jso/impl/JSBodyBloatedEmitter.java
similarity index 99%
rename from teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JSBodyBloatedEmitter.java
rename to teavm-jso-impl/src/main/java/org/teavm/jso/impl/JSBodyBloatedEmitter.java
index fdfc07b7d..72a26288c 100644
--- a/teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JSBodyBloatedEmitter.java
+++ b/teavm-jso-impl/src/main/java/org/teavm/jso/impl/JSBodyBloatedEmitter.java
@@ -13,7 +13,7 @@
  *  See the License for the specific language governing permissions and
  *  limitations under the License.
  */
-package org.teavm.jso.plugin;
+package org.teavm.jso.impl;
 
 import java.io.IOException;
 import org.teavm.codegen.SourceWriter;
diff --git a/teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JSBodyEmitter.java b/teavm-jso-impl/src/main/java/org/teavm/jso/impl/JSBodyEmitter.java
similarity index 97%
rename from teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JSBodyEmitter.java
rename to teavm-jso-impl/src/main/java/org/teavm/jso/impl/JSBodyEmitter.java
index f793f765e..b2a51273f 100644
--- a/teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JSBodyEmitter.java
+++ b/teavm-jso-impl/src/main/java/org/teavm/jso/impl/JSBodyEmitter.java
@@ -13,7 +13,7 @@
  *  See the License for the specific language governing permissions and
  *  limitations under the License.
  */
-package org.teavm.jso.plugin;
+package org.teavm.jso.impl;
 
 import java.io.IOException;
 import org.teavm.codegen.SourceWriter;
diff --git a/teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JSBodyGenerator.java b/teavm-jso-impl/src/main/java/org/teavm/jso/impl/JSBodyGenerator.java
similarity index 98%
rename from teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JSBodyGenerator.java
rename to teavm-jso-impl/src/main/java/org/teavm/jso/impl/JSBodyGenerator.java
index f97b4f0ee..b154cd9f8 100644
--- a/teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JSBodyGenerator.java
+++ b/teavm-jso-impl/src/main/java/org/teavm/jso/impl/JSBodyGenerator.java
@@ -13,7 +13,7 @@
  *  See the License for the specific language governing permissions and
  *  limitations under the License.
  */
-package org.teavm.jso.plugin;
+package org.teavm.jso.impl;
 
 import java.io.IOException;
 import org.teavm.codegen.SourceWriter;
diff --git a/teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JSBodyInlineUtil.java b/teavm-jso-impl/src/main/java/org/teavm/jso/impl/JSBodyInlineUtil.java
similarity index 99%
rename from teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JSBodyInlineUtil.java
rename to teavm-jso-impl/src/main/java/org/teavm/jso/impl/JSBodyInlineUtil.java
index 509387e30..716d0a119 100644
--- a/teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JSBodyInlineUtil.java
+++ b/teavm-jso-impl/src/main/java/org/teavm/jso/impl/JSBodyInlineUtil.java
@@ -13,7 +13,7 @@
  *  See the License for the specific language governing permissions and
  *  limitations under the License.
  */
-package org.teavm.jso.plugin;
+package org.teavm.jso.impl;
 
 import java.util.HashMap;
 import java.util.Map;
diff --git a/teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JSBodyRef.java b/teavm-jso-impl/src/main/java/org/teavm/jso/impl/JSBodyRef.java
similarity index 96%
rename from teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JSBodyRef.java
rename to teavm-jso-impl/src/main/java/org/teavm/jso/impl/JSBodyRef.java
index 6138a2313..6fb271ba4 100644
--- a/teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JSBodyRef.java
+++ b/teavm-jso-impl/src/main/java/org/teavm/jso/impl/JSBodyRef.java
@@ -13,7 +13,7 @@
  *  See the License for the specific language governing permissions and
  *  limitations under the License.
  */
-package org.teavm.jso.plugin;
+package org.teavm.jso.impl;
 
 import java.lang.annotation.ElementType;
 import java.lang.annotation.Retention;
diff --git a/teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JSBodyRepository.java b/teavm-jso-impl/src/main/java/org/teavm/jso/impl/JSBodyRepository.java
similarity index 97%
rename from teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JSBodyRepository.java
rename to teavm-jso-impl/src/main/java/org/teavm/jso/impl/JSBodyRepository.java
index 9f81cb6ea..dee6d002b 100644
--- a/teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JSBodyRepository.java
+++ b/teavm-jso-impl/src/main/java/org/teavm/jso/impl/JSBodyRepository.java
@@ -13,7 +13,7 @@
  *  See the License for the specific language governing permissions and
  *  limitations under the License.
  */
-package org.teavm.jso.plugin;
+package org.teavm.jso.impl;
 
 import java.util.HashMap;
 import java.util.HashSet;
diff --git a/teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JavascriptNativeProcessor.java b/teavm-jso-impl/src/main/java/org/teavm/jso/impl/JSClassProcessor.java
similarity index 95%
rename from teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JavascriptNativeProcessor.java
rename to teavm-jso-impl/src/main/java/org/teavm/jso/impl/JSClassProcessor.java
index 25e0d665c..bbb4bae90 100644
--- a/teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JavascriptNativeProcessor.java
+++ b/teavm-jso-impl/src/main/java/org/teavm/jso/impl/JSClassProcessor.java
@@ -13,7 +13,7 @@
  *  See the License for the specific language governing permissions and
  *  limitations under the License.
  */
-package org.teavm.jso.plugin;
+package org.teavm.jso.impl;
 
 import java.io.IOException;
 import java.io.StringReader;
@@ -78,18 +78,18 @@ import org.teavm.model.util.ProgramUtils;
  *
  * @author Alexey Andreev
  */
-class JavascriptNativeProcessor {
+class JSClassProcessor {
     private ClassReaderSource classSource;
     private Program program;
     private List<Instruction> replacement = new ArrayList<>();
-    private NativeJavascriptClassRepository nativeRepos;
+    private JSTypeHelper typeHelper;
     private Diagnostics diagnostics;
     private int methodIndexGenerator;
     private Map<MethodReference, MethodReader> overridenMethodCache = new HashMap<>();
 
-    public JavascriptNativeProcessor(ClassReaderSource classSource) {
+    public JSClassProcessor(ClassReaderSource classSource) {
         this.classSource = classSource;
-        nativeRepos = new NativeJavascriptClassRepository(classSource);
+        typeHelper = new JSTypeHelper(classSource);
     }
 
     public ClassReaderSource getClassSource() {
@@ -97,11 +97,11 @@ class JavascriptNativeProcessor {
     }
 
     public boolean isNative(String className) {
-        return nativeRepos.isJavaScriptClass(className);
+        return typeHelper.isJavaScriptClass(className);
     }
 
     public boolean isNativeImplementation(String className) {
-        return nativeRepos.isJavaScriptImplementation(className);
+        return typeHelper.isJavaScriptImplementation(className);
     }
 
     public void setDiagnostics(Diagnostics diagnostics) {
@@ -109,7 +109,7 @@ class JavascriptNativeProcessor {
     }
 
     public MethodReference isFunctor(String className) {
-        if (!nativeRepos.isJavaScriptImplementation(className)) {
+        if (!typeHelper.isJavaScriptImplementation(className)) {
             return null;
         }
         ClassReader cls = classSource.get(className);
@@ -138,7 +138,7 @@ class JavascriptNativeProcessor {
     public void processClass(ClassHolder cls) {
         Set<MethodDescriptor> preservedMethods = new HashSet<>();
         for (String iface : cls.getInterfaces()) {
-            if (nativeRepos.isJavaScriptClass(iface)) {
+            if (typeHelper.isJavaScriptClass(iface)) {
                 addPreservedMethods(iface, preservedMethods);
             }
         }
@@ -314,7 +314,7 @@ class JavascriptNativeProcessor {
             return processJSBodyInvocation(repository, method, callLocation, invoke);
         }
 
-        if (!nativeRepos.isJavaScriptClass(invoke.getMethod().getClassName())) {
+        if (!typeHelper.isJavaScriptClass(invoke.getMethod().getClassName())) {
             return false;
         }
 
@@ -452,14 +452,14 @@ class JavascriptNativeProcessor {
                 name = redefinedMethodName.getString();
             }
         }
-        if (method.getResultType() != ValueType.VOID && !isSupportedType(method.getResultType())) {
+        if (method.getResultType() != ValueType.VOID && !typeHelper.isSupportedType(method.getResultType())) {
             diagnostics.error(callLocation, "Method {{m0}} is not a proper native JavaScript method "
                     + "declaration", invoke.getMethod());
             return false;
         }
 
         for (ValueType arg : method.getParameterTypes()) {
-            if (!isSupportedType(arg)) {
+            if (!typeHelper.isSupportedType(arg)) {
                 diagnostics.error(callLocation, "Method {{m0}} is not a proper native JavaScript method "
                         + "or constructor declaration", invoke.getMethod());
                 return false;
@@ -521,12 +521,13 @@ class JavascriptNativeProcessor {
         if (!isStatic) {
             ValueType paramType = ValueType.object(methodToProcess.getOwnerName());
             paramTypes[offset++] = paramType;
-            if (!isSupportedType(paramType)) {
+            if (!typeHelper.isSupportedType(paramType)) {
                 diagnostics.error(location, "Non-static JSBody method {{m0}} is owned by non-JS class {{c1}}",
                         methodToProcess.getReference(), methodToProcess.getOwnerName());
             }
         }
-        if (methodToProcess.getResultType() != ValueType.VOID && !isSupportedType(methodToProcess.getResultType())) {
+        if (methodToProcess.getResultType() != ValueType.VOID
+                && !typeHelper.isSupportedType(methodToProcess.getResultType())) {
             diagnostics.error(location, "JSBody method {{m0}} returns unsupported type {{t1}}",
                     methodToProcess.getReference(), methodToProcess.getResultType());
         }
@@ -579,8 +580,9 @@ class JavascriptNativeProcessor {
             } else {
                 expr = rootNode;
             }
-            JavaInvocationValidator javaValidator = new JavaInvocationValidator(classSource, diagnostics);
-            javaValidator.validate(location, expr);
+            JavaInvocationProcessor javaInvocationProcessor = new JavaInvocationProcessor(typeHelper,
+                    classSource, diagnostics);
+            javaInvocationProcessor.validate(location, expr);
             repository.emitters.put(proxyMethod, new JSBodyAstEmitter(isStatic, expr, parameterNames));
         }
         repository.methodMap.put(methodToProcess.getReference(), proxyMethod);
@@ -1078,7 +1080,7 @@ class JavascriptNativeProcessor {
     }
 
     private boolean isProperGetter(MethodDescriptor desc) {
-        if (desc.parameterCount() > 0 || !isSupportedType(desc.getResultType())) {
+        if (desc.parameterCount() > 0 || !typeHelper.isSupportedType(desc.getResultType())) {
             return false;
         }
         if (desc.getResultType().equals(ValueType.BOOLEAN)) {
@@ -1090,7 +1092,7 @@ class JavascriptNativeProcessor {
     }
 
     private boolean isProperSetter(MethodDescriptor desc) {
-        if (desc.parameterCount() != 1 || !isSupportedType(desc.parameterType(0))
+        if (desc.parameterCount() != 1 || !typeHelper.isSupportedType(desc.parameterType(0))
                 || desc.getResultType() != ValueType.VOID) {
             return false;
         }
@@ -1106,13 +1108,13 @@ class JavascriptNativeProcessor {
     }
 
     private boolean isProperGetIndexer(MethodDescriptor desc) {
-        return desc.parameterCount() == 1 && isSupportedType(desc.parameterType(0))
-                && isSupportedType(desc.getResultType());
+        return desc.parameterCount() == 1 && typeHelper.isSupportedType(desc.parameterType(0))
+                && typeHelper.isSupportedType(desc.getResultType());
     }
 
     private boolean isProperSetIndexer(MethodDescriptor desc) {
-        return desc.parameterCount() == 2 && isSupportedType(desc.parameterType(0))
-                && isSupportedType(desc.parameterType(0)) && desc.getResultType() == ValueType.VOID;
+        return desc.parameterCount() == 2 && typeHelper.isSupportedType(desc.parameterType(0))
+                && typeHelper.isSupportedType(desc.parameterType(0)) && desc.getResultType() == ValueType.VOID;
     }
 
     private String cutPrefix(String name, int prefixLength) {
@@ -1125,25 +1127,4 @@ class JavascriptNativeProcessor {
         }
         return Character.toLowerCase(name.charAt(prefixLength)) + name.substring(prefixLength + 1);
     }
-
-    private boolean isSupportedType(ValueType type) {
-        if (type == ValueType.VOID) {
-            return false;
-        }
-        if (type instanceof ValueType.Primitive) {
-            switch (((ValueType.Primitive) type).getKind()) {
-                case LONG:
-                    return false;
-                default:
-                    return true;
-            }
-        } else if (type instanceof ValueType.Array) {
-            return isSupportedType(((ValueType.Array) type).getItemType());
-        } else if (type instanceof ValueType.Object) {
-            String typeName = ((ValueType.Object) type).getClassName();
-            return typeName.equals("java.lang.String") || nativeRepos.isJavaScriptClass(typeName);
-        } else {
-            return false;
-        }
-    }
 }
diff --git a/teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JSODependencyListener.java b/teavm-jso-impl/src/main/java/org/teavm/jso/impl/JSDependencyListener.java
similarity index 98%
rename from teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JSODependencyListener.java
rename to teavm-jso-impl/src/main/java/org/teavm/jso/impl/JSDependencyListener.java
index 253540b1c..826794fac 100644
--- a/teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JSODependencyListener.java
+++ b/teavm-jso-impl/src/main/java/org/teavm/jso/impl/JSDependencyListener.java
@@ -13,7 +13,7 @@
  *  See the License for the specific language governing permissions and
  *  limitations under the License.
  */
-package org.teavm.jso.plugin;
+package org.teavm.jso.impl;
 
 import java.util.HashMap;
 import java.util.HashSet;
@@ -38,7 +38,7 @@ import org.teavm.model.MethodReader;
  *
  * @author Alexey Andreev
  */
-class JSODependencyListener extends AbstractDependencyListener {
+class JSDependencyListener extends AbstractDependencyListener {
     private Map<String, ExposedClass> exposedClasses = new HashMap<>();
     private ClassReaderSource classSource;
     private DependencyAgent agent;
diff --git a/teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JSNativeGenerator.java b/teavm-jso-impl/src/main/java/org/teavm/jso/impl/JSNativeGenerator.java
similarity index 99%
rename from teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JSNativeGenerator.java
rename to teavm-jso-impl/src/main/java/org/teavm/jso/impl/JSNativeGenerator.java
index 44d64c0a0..685a12f00 100644
--- a/teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JSNativeGenerator.java
+++ b/teavm-jso-impl/src/main/java/org/teavm/jso/impl/JSNativeGenerator.java
@@ -13,7 +13,7 @@
  *  See the License for the specific language governing permissions and
  *  limitations under the License.
  */
-package org.teavm.jso.plugin;
+package org.teavm.jso.impl;
 
 import java.io.IOException;
 import org.teavm.codegen.SourceWriter;
diff --git a/teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JSOPlugin.java b/teavm-jso-impl/src/main/java/org/teavm/jso/impl/JSOPlugin.java
similarity index 84%
rename from teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JSOPlugin.java
rename to teavm-jso-impl/src/main/java/org/teavm/jso/impl/JSOPlugin.java
index c23a98465..d01e1c8bc 100644
--- a/teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JSOPlugin.java
+++ b/teavm-jso-impl/src/main/java/org/teavm/jso/impl/JSOPlugin.java
@@ -13,7 +13,7 @@
  *  See the License for the specific language governing permissions and
  *  limitations under the License.
  */
-package org.teavm.jso.plugin;
+package org.teavm.jso.impl;
 
 import org.teavm.vm.spi.TeaVMHost;
 import org.teavm.vm.spi.TeaVMPlugin;
@@ -28,8 +28,8 @@ public class JSOPlugin implements TeaVMPlugin {
         JSBodyRepository repository = new JSBodyRepository();
         host.registerService(JSBodyRepository.class, repository);
         host.add(new JSObjectClassTransformer(repository));
-        JSODependencyListener dependencyListener = new JSODependencyListener();
-        JSOAliasRenderer aliasRenderer = new JSOAliasRenderer(dependencyListener);
+        JSDependencyListener dependencyListener = new JSDependencyListener();
+        JSAliasRenderer aliasRenderer = new JSAliasRenderer(dependencyListener);
         host.add(dependencyListener);
         host.add(aliasRenderer);
     }
diff --git a/teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JSObjectClassTransformer.java b/teavm-jso-impl/src/main/java/org/teavm/jso/impl/JSObjectClassTransformer.java
similarity index 93%
rename from teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JSObjectClassTransformer.java
rename to teavm-jso-impl/src/main/java/org/teavm/jso/impl/JSObjectClassTransformer.java
index b6ba5e1a2..323bc3e54 100644
--- a/teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JSObjectClassTransformer.java
+++ b/teavm-jso-impl/src/main/java/org/teavm/jso/impl/JSObjectClassTransformer.java
@@ -13,7 +13,7 @@
  *  See the License for the specific language governing permissions and
  *  limitations under the License.
  */
-package org.teavm.jso.plugin;
+package org.teavm.jso.impl;
 
 import org.teavm.diagnostics.Diagnostics;
 import org.teavm.model.ClassHolder;
@@ -27,7 +27,7 @@ import org.teavm.model.MethodReference;
  * @author Alexey Andreev
  */
 public class JSObjectClassTransformer implements ClassHolderTransformer {
-    private JavascriptNativeProcessor processor;
+    private JSClassProcessor processor;
     private JSBodyRepository repository;
 
     public JSObjectClassTransformer(JSBodyRepository repository) {
@@ -37,7 +37,7 @@ public class JSObjectClassTransformer implements ClassHolderTransformer {
     @Override
     public void transformClass(ClassHolder cls, ClassReaderSource innerSource, Diagnostics diagnostics) {
         if (processor == null || processor.getClassSource() != innerSource) {
-            processor = new JavascriptNativeProcessor(innerSource);
+            processor = new JSClassProcessor(innerSource);
         }
         processor.setDiagnostics(diagnostics);
         processor.processClass(cls);
diff --git a/teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JSParser.java b/teavm-jso-impl/src/main/java/org/teavm/jso/impl/JSParser.java
similarity index 97%
rename from teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JSParser.java
rename to teavm-jso-impl/src/main/java/org/teavm/jso/impl/JSParser.java
index 362cb9221..ade564f57 100644
--- a/teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JSParser.java
+++ b/teavm-jso-impl/src/main/java/org/teavm/jso/impl/JSParser.java
@@ -13,7 +13,7 @@
  *  See the License for the specific language governing permissions and
  *  limitations under the License.
  */
-package org.teavm.jso.plugin;
+package org.teavm.jso.impl;
 
 import org.mozilla.javascript.CompilerEnvirons;
 import org.mozilla.javascript.ErrorReporter;
diff --git a/teavm-jso-impl/src/main/java/org/teavm/jso/plugin/NativeJavascriptClassRepository.java b/teavm-jso-impl/src/main/java/org/teavm/jso/impl/JSTypeHelper.java
similarity index 76%
rename from teavm-jso-impl/src/main/java/org/teavm/jso/plugin/NativeJavascriptClassRepository.java
rename to teavm-jso-impl/src/main/java/org/teavm/jso/impl/JSTypeHelper.java
index 52f15a137..f15a09aa8 100644
--- a/teavm-jso-impl/src/main/java/org/teavm/jso/plugin/NativeJavascriptClassRepository.java
+++ b/teavm-jso-impl/src/main/java/org/teavm/jso/impl/JSTypeHelper.java
@@ -13,7 +13,7 @@
  *  See the License for the specific language governing permissions and
  *  limitations under the License.
  */
-package org.teavm.jso.plugin;
+package org.teavm.jso.impl;
 
 import java.util.HashMap;
 import java.util.Map;
@@ -21,17 +21,18 @@ import org.teavm.jso.JSObject;
 import org.teavm.model.ClassReader;
 import org.teavm.model.ClassReaderSource;
 import org.teavm.model.ElementModifier;
+import org.teavm.model.ValueType;
 
 /**
  *
  * @author Alexey Andreev
  */
-class NativeJavascriptClassRepository {
+class JSTypeHelper {
     private ClassReaderSource classSource;
     private Map<String, Boolean> knownJavaScriptClasses = new HashMap<>();
     private Map<String, Boolean> knownJavaScriptImplementations = new HashMap<>();
 
-    public NativeJavascriptClassRepository(ClassReaderSource classSource) {
+    public JSTypeHelper(ClassReaderSource classSource) {
         this.classSource = classSource;
         knownJavaScriptClasses.put(JSObject.class.getName(), true);
     }
@@ -82,4 +83,25 @@ class NativeJavascriptClassRepository {
         }
         return cls.getInterfaces().stream().anyMatch(iface -> isJavaScriptClass(iface));
     }
+
+    public boolean isSupportedType(ValueType type) {
+        if (type == ValueType.VOID) {
+            return false;
+        }
+        if (type instanceof ValueType.Primitive) {
+            switch (((ValueType.Primitive) type).getKind()) {
+                case LONG:
+                    return false;
+                default:
+                    return true;
+            }
+        } else if (type instanceof ValueType.Array) {
+            return isSupportedType(((ValueType.Array) type).getItemType());
+        } else if (type instanceof ValueType.Object) {
+            String typeName = ((ValueType.Object) type).getClassName();
+            return typeName.equals("java.lang.String") || isJavaScriptClass(typeName);
+        } else {
+            return false;
+        }
+    }
 }
diff --git a/teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JavaInvocationValidator.java b/teavm-jso-impl/src/main/java/org/teavm/jso/impl/JavaInvocationProcessor.java
similarity index 95%
rename from teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JavaInvocationValidator.java
rename to teavm-jso-impl/src/main/java/org/teavm/jso/impl/JavaInvocationProcessor.java
index a0ab73e96..a469f5dc8 100644
--- a/teavm-jso-impl/src/main/java/org/teavm/jso/plugin/JavaInvocationValidator.java
+++ b/teavm-jso-impl/src/main/java/org/teavm/jso/impl/JavaInvocationProcessor.java
@@ -13,7 +13,7 @@
  *  See the License for the specific language governing permissions and
  *  limitations under the License.
  */
-package org.teavm.jso.plugin;
+package org.teavm.jso.impl;
 
 import org.mozilla.javascript.Token;
 import org.mozilla.javascript.ast.AstNode;
@@ -34,12 +34,14 @@ import org.teavm.model.MethodReference;
  *
  * @author Alexey Andreev
  */
-class JavaInvocationValidator implements NodeVisitor {
+class JavaInvocationProcessor implements NodeVisitor {
     private ClassReaderSource classSource;
+    private JSTypeHelper typeHelper;
     private Diagnostics diagnostics;
     private CallLocation location;
 
-    public JavaInvocationValidator(ClassReaderSource classSource, Diagnostics diagnostics) {
+    public JavaInvocationProcessor(JSTypeHelper typeHelper, ClassReaderSource classSource, Diagnostics diagnostics) {
+        this.typeHelper = typeHelper;
         this.classSource = classSource;
         this.diagnostics = diagnostics;
     }
diff --git a/teavm-jso-impl/src/main/java/org/teavm/jso/plugin/NameEmitter.java b/teavm-jso-impl/src/main/java/org/teavm/jso/impl/NameEmitter.java
similarity index 96%
rename from teavm-jso-impl/src/main/java/org/teavm/jso/plugin/NameEmitter.java
rename to teavm-jso-impl/src/main/java/org/teavm/jso/impl/NameEmitter.java
index 8e5206a89..45f759b0e 100644
--- a/teavm-jso-impl/src/main/java/org/teavm/jso/plugin/NameEmitter.java
+++ b/teavm-jso-impl/src/main/java/org/teavm/jso/impl/NameEmitter.java
@@ -13,7 +13,7 @@
  *  See the License for the specific language governing permissions and
  *  limitations under the License.
  */
-package org.teavm.jso.plugin;
+package org.teavm.jso.impl;
 
 import java.io.IOException;
 
diff --git a/teavm-jso-impl/src/main/java/org/teavm/jso/plugin/TeaVMErrorReporter.java b/teavm-jso-impl/src/main/java/org/teavm/jso/impl/TeaVMErrorReporter.java
similarity index 98%
rename from teavm-jso-impl/src/main/java/org/teavm/jso/plugin/TeaVMErrorReporter.java
rename to teavm-jso-impl/src/main/java/org/teavm/jso/impl/TeaVMErrorReporter.java
index 4bd2b816a..0251b8d2c 100644
--- a/teavm-jso-impl/src/main/java/org/teavm/jso/plugin/TeaVMErrorReporter.java
+++ b/teavm-jso-impl/src/main/java/org/teavm/jso/impl/TeaVMErrorReporter.java
@@ -13,7 +13,7 @@
  *  See the License for the specific language governing permissions and
  *  limitations under the License.
  */
-package org.teavm.jso.plugin;
+package org.teavm.jso.impl;
 
 import org.mozilla.javascript.ErrorReporter;
 import org.mozilla.javascript.EvaluatorException;
diff --git a/teavm-jso-impl/src/main/resources/META-INF/services/org.teavm.vm.spi.TeaVMPlugin b/teavm-jso-impl/src/main/resources/META-INF/services/org.teavm.vm.spi.TeaVMPlugin
index c0f1b934e..16e195758 100644
--- a/teavm-jso-impl/src/main/resources/META-INF/services/org.teavm.vm.spi.TeaVMPlugin
+++ b/teavm-jso-impl/src/main/resources/META-INF/services/org.teavm.vm.spi.TeaVMPlugin
@@ -1 +1 @@
-org.teavm.jso.plugin.JSOPlugin
\ No newline at end of file
+org.teavm.jso.impl.JSOPlugin
\ No newline at end of file
diff --git a/teavm-jso-impl/src/test/java/org/teavm/jso/plugin/AstWriterTest.java b/teavm-jso-impl/src/test/java/org/teavm/jso/plugin/AstWriterTest.java
index 22b786acd..3ebc273d1 100644
--- a/teavm-jso-impl/src/test/java/org/teavm/jso/plugin/AstWriterTest.java
+++ b/teavm-jso-impl/src/test/java/org/teavm/jso/plugin/AstWriterTest.java
@@ -25,6 +25,8 @@ import org.mozilla.javascript.Context;
 import org.mozilla.javascript.ast.AstRoot;
 import org.teavm.codegen.SourceWriter;
 import org.teavm.codegen.SourceWriterBuilder;
+import org.teavm.jso.impl.AstWriter;
+import org.teavm.jso.impl.JSParser;
 
 /**
  *