jso: improve support of instanceof and cast against JS wrapper types

Fix #808

core/src/main/resources/org/teavm/backend/javascript/exception.js

@@ -125,6 +125,13 @@ let $rt_throwCCE = () => teavm_javaConstructorExists("java.lang.ClassCastExcepti
     ? $rt_throw(teavm_javaConstructor("java.lang.ClassCastException", "()V")())
     : $rt_throw($rt_createException($rt_str("")));
 
+let $rt_throwCCEIfFalse = (value, o) => {
+    if (!value) {
+        $rt_throwCCE();
+    }
+    return o;
+}
+
 let $rt_createStackElement = (className, methodName, fileName, lineNumber) => {
     if (teavm_javaConstructorExists("java.lang.StackTraceElement",
         "(Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;I)V")) {

jso/apis/src/main/java/org/teavm/jso/core/JSBoolean.java

@@ -18,7 +18,9 @@ package org.teavm.jso.core;
 import org.teavm.interop.NoSideEffects;
 import org.teavm.jso.JSBody;
 import org.teavm.jso.JSObject;
+import org.teavm.jso.JSPrimitiveType;
 
+@JSPrimitiveType("boolean")
 public abstract class JSBoolean implements JSObject {
     private JSBoolean() {
     }

jso/apis/src/main/java/org/teavm/jso/core/JSError.java

@@ -16,11 +16,19 @@
 package org.teavm.jso.core;
 
 import org.teavm.jso.JSBody;
+import org.teavm.jso.JSClass;
 import org.teavm.jso.JSFunctor;
 import org.teavm.jso.JSObject;
 import org.teavm.jso.JSProperty;
 
-public abstract class JSError implements JSObject {
+@JSClass(name = "Error")
+public class JSError implements JSObject {
+    public JSError() {
+    }
+
+    public JSError(String message) {
+    }
+
     @JSBody(params = { "tryClause", "catchClause" }, script = ""
             + "try {"
                 + "return tryClause();"
@@ -29,17 +37,19 @@ public abstract class JSError implements JSObject {
             + "}")
     public static native <T> T catchNative(TryClause<T> tryClause, CatchClause<T> catchClause);
 
-    @JSBody(params = "object", script = "return object instanceof Error;")
+    @Deprecated
-    public static native boolean isError(JSObject object);
+    public static boolean isError(JSObject object) {
+        return object instanceof JSError;
+    }
 
     @JSProperty
-    public abstract String getStack();
+    public native String getStack();
 
     @JSProperty
-    public abstract String getMessage();
+    public native String getMessage();
 
     @JSProperty
-    public abstract String getName();
+    public native String getName();
 
     @JSFunctor
     public interface TryClause<T> extends JSObject {

jso/apis/src/main/java/org/teavm/jso/core/JSFunction.java

@@ -17,8 +17,10 @@ package org.teavm.jso.core;
 
 import org.teavm.jso.JSByRef;
 import org.teavm.jso.JSObject;
+import org.teavm.jso.JSPrimitiveType;
 import org.teavm.jso.JSProperty;
 
+@JSPrimitiveType("function")
 public abstract class JSFunction implements JSObject {
     @JSProperty
     public abstract int getLength();

jso/apis/src/main/java/org/teavm/jso/core/JSNumber.java

@@ -18,7 +18,9 @@ package org.teavm.jso.core;
 import org.teavm.interop.NoSideEffects;
 import org.teavm.jso.JSBody;
 import org.teavm.jso.JSObject;
+import org.teavm.jso.JSPrimitiveType;
 
+@JSPrimitiveType("number")
 public abstract class JSNumber implements JSObject {
     private JSNumber() {
     }

jso/apis/src/main/java/org/teavm/jso/core/JSObjects.java

@@ -43,13 +43,14 @@ public final class JSObjects {
     @NoSideEffects
     public static native <T extends JSObject> T createWithoutProto();
 
-    @JSBody(params = "object", script = "return typeof object === 'undefined';")
+    public static boolean isUndefined(Object object) {
-    @NoSideEffects
+        return object instanceof JSUndefined;
-    public static native boolean isUndefined(Object object);
+    }
 
-    @JSBody(script = "return void 0;")
+    @Deprecated
-    @NoSideEffects
+    public static JSObject undefined() {
-    public static native JSObject undefined();
+        return JSUndefined.instance();
+    }
 
     @JSBody(params = "object", script = "return typeof object;")
     @NoSideEffects

jso/apis/src/main/java/org/teavm/jso/core/JSString.java

@@ -18,8 +18,10 @@ package org.teavm.jso.core;
 import org.teavm.interop.NoSideEffects;
 import org.teavm.jso.JSBody;
 import org.teavm.jso.JSObject;
+import org.teavm.jso.JSPrimitiveType;
 import org.teavm.jso.JSProperty;
 
+@JSPrimitiveType("string")
 public abstract class JSString implements JSObject {
     private JSString() {
     }

jso/apis/src/main/java/org/teavm/jso/core/JSSymbol.java

@@ -17,8 +17,11 @@ package org.teavm.jso.core;
 
 import org.teavm.interop.NoSideEffects;
 import org.teavm.jso.JSBody;
+import org.teavm.jso.JSIndexer;
 import org.teavm.jso.JSObject;
+import org.teavm.jso.JSPrimitiveType;
 
+@JSPrimitiveType("symbol")
 public class JSSymbol<T> implements JSObject {
     private JSSymbol() {
     }
@@ -26,10 +29,10 @@ public class JSSymbol<T> implements JSObject {
     @JSBody(params = "name", script = "return Symbol(name);")
     public static native <T> JSSymbol<T> create(String name);
 
-    @JSBody(params = "obj", script = "return obj[this];")
+    @JSIndexer
     public native T get(Object obj);
 
-    @JSBody(params = { "obj", "value" }, script = "obj[this] = value;")
+    @JSIndexer
     @NoSideEffects
     public native void set(Object obj, T value);
 }

jso/apis/src/main/java/org/teavm/jso/core/JSUndefined.java

@@ -0,0 +1,33 @@
+/*
+ *  Copyright 2024 Alexey Andreev.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *       http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.teavm.jso.core;
+
+import org.teavm.interop.NoSideEffects;
+import org.teavm.jso.JSBody;
+import org.teavm.jso.JSClass;
+import org.teavm.jso.JSObject;
+import org.teavm.jso.JSPrimitiveType;
+
+@JSClass
+@JSPrimitiveType("undefined")
+public class JSUndefined implements JSObject {
+    private JSUndefined() {
+    }
+
+    @JSBody(script = "return void 0;")
+    @NoSideEffects
+    public static native JSUndefined instance();
+}

jso/core/src/main/java/org/teavm/jso/JSClass.java

@@ -24,4 +24,6 @@ import java.lang.annotation.Target;
 @Target(ElementType.TYPE)
 public @interface JSClass {
     String name() default "";
+
+    boolean transparent() default false;
 }

jso/core/src/main/java/org/teavm/jso/JSPrimitiveType.java

@@ -0,0 +1,27 @@
+/*
+ *  Copyright 2024 Alexey Andreev.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *       http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.teavm.jso;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+@Retention(RetentionPolicy.RUNTIME)
+@Target(ElementType.TYPE)
+public @interface JSPrimitiveType {
+    String value();
+}

jso/impl/src/main/java/org/teavm/jso/impl/JS.java

@@ -704,4 +704,16 @@ final class JS {
     @InjectedBy(JSNativeInjector.class)
     @NoSideEffects
     public static native JSObject importModule(String name);
+
+    @InjectedBy(JSNativeInjector.class)
+    @NoSideEffects
+    public static native boolean instanceOf(JSObject obj, JSObject cls);
+
+    @InjectedBy(JSNativeInjector.class)
+    @NoSideEffects
+    public static native boolean isPrimitive(JSObject obj, JSObject primitive);
+
+    @InjectedBy(JSNativeInjector.class)
+    @NoSideEffects
+    public static native JSObject throwCCEIfFalse(boolean value, JSObject o);
 }

jso/impl/src/main/java/org/teavm/jso/impl/JSClassProcessor.java

@@ -35,8 +35,10 @@ import org.teavm.diagnostics.Diagnostics;
 import org.teavm.interop.NoSideEffects;
 import org.teavm.jso.JSBody;
 import org.teavm.jso.JSByRef;
+import org.teavm.jso.JSClass;
 import org.teavm.jso.JSFunctor;
 import org.teavm.jso.JSObject;
+import org.teavm.jso.JSPrimitiveType;
 import org.teavm.model.AnnotationContainerReader;
 import org.teavm.model.AnnotationHolder;
 import org.teavm.model.AnnotationReader;
@@ -86,6 +88,10 @@ class JSClassProcessor {
             Object.class, JSObject.class);
     private static final MethodReference IS_JS = new MethodReference(JSWrapper.class, "isJs",
             Object.class, boolean.class);
+    private static final MethodReference IS_PRIMITIVE = new MethodReference(JSWrapper.class, "isPrimitive",
+            Object.class, JSObject.class, boolean.class);
+    private static final MethodReference INSTANCE_OF = new MethodReference(JSWrapper.class, "instanceOf",
+            Object.class, JSObject.class, boolean.class);
     private final ClassReaderSource classSource;
     private final JSBodyRepository repository;
     private final JavaInvocationProcessor javaInvocationProcessor;
@@ -470,11 +476,23 @@ class JSClassProcessor {
 
         ClassReader targetClass = classSource.get(targetClassName);
         if (targetClass.getAnnotations().get(JSFunctor.class.getName()) == null) {
-            AssignInstruction assign = new AssignInstruction();
+            if (isTransparent(targetClassName)) {
-            assign.setLocation(location.getSourceLocation());
+                var assign = new AssignInstruction();
-            assign.setAssignee(cast.getValue());
+                assign.setLocation(location.getSourceLocation());
-            assign.setReceiver(cast.getReceiver());
+                assign.setAssignee(cast.getValue());
-            replacement.add(assign);
+                assign.setReceiver(cast.getReceiver());
+                replacement.add(assign);
+            } else {
+                var instanceOfResult = program.createVariable();
+                processIsInstanceUnwrapped(cast.getLocation(), cast.getValue(), targetClassName, instanceOfResult);
+
+                var invoke = new InvokeInstruction();
+                invoke.setType(InvocationType.SPECIAL);
+                invoke.setMethod(JSMethods.THROW_CCE_IF_FALSE);
+                invoke.setArguments(instanceOfResult, cast.getValue());
+                invoke.setReceiver(cast.getReceiver());
+                replacement.add(invoke);
+            }
             return true;
         }
 
@@ -499,23 +517,107 @@ class JSClassProcessor {
             return;
         }
 
-        var type = types.typeOf(isInstance.getValue());
+        replacement.clear();
-        if (type == JSType.JS) {
+        processIsInstance(isInstance.getLocation(), types.typeOf(isInstance.getValue()), isInstance.getValue(),
-            var replacement = new IntegerConstantInstruction();
+                targetClassName, isInstance.getReceiver());
-            replacement.setConstant(1);
+        isInstance.insertPreviousAll(replacement);
-            replacement.setReceiver(isInstance.getReceiver());
+        isInstance.delete();
-            replacement.setLocation(isInstance.getLocation());
+        replacement.clear();
-            isInstance.replace(replacement);
+    }
-            return;
-        }
 
-        var replacement = new InvokeInstruction();
+    private void processIsInstance(TextLocation location, JSType type, Variable value, String targetClassName,
-        replacement.setType(InvocationType.SPECIAL);
+            Variable receiver) {
-        replacement.setMethod(IS_JS);
+        if (type == JSType.JS) {
-        replacement.setArguments(isInstance.getValue());
+            if (isTransparent(targetClassName)) {
-        replacement.setReceiver(isInstance.getReceiver());
+                var cst = new IntegerConstantInstruction();
-        replacement.setLocation(isInstance.getLocation());
+                cst.setConstant(1);
-        isInstance.replace(replacement);
+                cst.setReceiver(receiver);
+                cst.setLocation(location);
+                replacement.add(cst);
+            } else {
+                var primitiveType = getPrimitiveType(targetClassName);
+                var invoke = new InvokeInstruction();
+                invoke.setType(InvocationType.SPECIAL);
+                invoke.setMethod(primitiveType != null ? JSMethods.IS_PRIMITIVE : JSMethods.INSTANCE_OF);
+                var secondArg = primitiveType != null
+                        ? marshaller.addJsString(primitiveType, location)
+                        : marshaller.classRef(targetClassName, location);
+                invoke.setArguments(value, secondArg);
+                invoke.setReceiver(receiver);
+                invoke.setLocation(location);
+                replacement.add(invoke);
+            }
+        } else {
+            if (isTransparent(targetClassName)) {
+                var invoke = new InvokeInstruction();
+                invoke.setType(InvocationType.SPECIAL);
+                invoke.setMethod(IS_JS);
+                invoke.setArguments(value);
+                invoke.setReceiver(receiver);
+                invoke.setLocation(location);
+                replacement.add(invoke);
+            } else {
+                var primitiveType = getPrimitiveType(targetClassName);
+                var invoke = new InvokeInstruction();
+                invoke.setType(InvocationType.SPECIAL);
+                invoke.setMethod(primitiveType != null ? IS_PRIMITIVE : INSTANCE_OF);
+                var secondArg = primitiveType != null
+                        ? marshaller.addJsString(primitiveType, location)
+                        : marshaller.classRef(targetClassName, location);
+                invoke.setArguments(value, secondArg);
+                invoke.setReceiver(receiver);
+                invoke.setLocation(location);
+                replacement.add(invoke);
+            }
+        }
+    }
+
+    private void processIsInstanceUnwrapped(TextLocation location, Variable value, String targetClassName,
+            Variable receiver) {
+        var primitiveType = getPrimitiveType(targetClassName);
+        var invoke = new InvokeInstruction();
+        invoke.setType(InvocationType.SPECIAL);
+        invoke.setMethod(primitiveType != null ? JSMethods.IS_PRIMITIVE : JSMethods.INSTANCE_OF);
+        var secondArg = primitiveType != null
+                ? marshaller.addJsString(primitiveType, location)
+                : marshaller.classRef(targetClassName, location);
+        invoke.setArguments(value, secondArg);
+        invoke.setReceiver(receiver);
+        invoke.setLocation(location);
+        replacement.add(invoke);
+    }
+
+    private boolean isTransparent(String className) {
+        var cls = classSource.get(className);
+        if (cls == null) {
+            return true;
+        }
+        if (cls.hasModifier(ElementModifier.INTERFACE)) {
+            return true;
+        }
+        var clsAnnot = cls.getAnnotations().get(JSClass.class.getName());
+        if (clsAnnot != null) {
+            var transparent = clsAnnot.getValue("transparent");
+            if (transparent != null) {
+                return transparent.getBoolean();
+            }
+        }
+        return false;
+    }
+
+    private String getPrimitiveType(String className) {
+        var cls = classSource.get(className);
+        if (cls == null) {
+            return null;
+        }
+        var clsAnnot = cls.getAnnotations().get(JSPrimitiveType.class.getName());
+        if (clsAnnot != null) {
+            var value = clsAnnot.getValue("value");
+            if (value != null) {
+                return value.getString();
+            }
+        }
+        return null;
     }
 
     private Variable wrapJsAsJava(Instruction instruction, Variable var, ValueType type) {

jso/impl/src/main/java/org/teavm/jso/impl/JSMethods.java

@@ -125,6 +125,13 @@ final class JSMethods {
     public static final MethodReference IMPORT_MODULE = new MethodReference(JS.class, "importModule",
             String.class, JSObject.class);
 
+    public static final MethodReference INSTANCE_OF = new MethodReference(JS.class, "instanceOf", JSObject.class,
+            JSObject.class, boolean.class);
+    public static final MethodReference IS_PRIMITIVE = new MethodReference(JS.class, "isPrimitive", JSObject.class,
+            JSObject.class, boolean.class);
+    public static final MethodReference THROW_CCE_IF_FALSE = new MethodReference(JS.class, "throwCCEIfFalse",
+            boolean.class, JSObject.class, JSObject.class);
+
     public static final ValueType JS_OBJECT = ValueType.object(JSObject.class.getName());
     public static final ValueType OBJECT = ValueType.object("java.lang.Object");
     public static final ValueType JS_ARRAY = ValueType.object(JSArray.class.getName());

jso/impl/src/main/java/org/teavm/jso/impl/JSNativeInjector.java

@@ -190,6 +190,41 @@ public class JSNativeInjector implements Injector, DependencyPlugin {
                 writer.appendFunction(context.importModule(name));
                 break;
             }
+            case "instanceOf": {
+                if (context.getPrecedence().ordinal() >= Precedence.CONDITIONAL.ordinal()) {
+                    writer.append("(");
+                }
+                context.writeExpr(context.getArgument(0), Precedence.COMPARISON.next());
+                writer.append(" instanceof ");
+                context.writeExpr(context.getArgument(1), Precedence.COMPARISON.next());
+                writer.ws().append("?").ws().append("1").ws().append(":").ws().append("0");
+                if (context.getPrecedence().ordinal() >= Precedence.CONDITIONAL.ordinal()) {
+                    writer.append(")");
+                }
+                break;
+            }
+            case "isPrimitive": {
+                if (context.getPrecedence().ordinal() >= Precedence.CONDITIONAL.ordinal()) {
+                    writer.append("(");
+                }
+                writer.append("typeof ");
+                context.writeExpr(context.getArgument(0), Precedence.UNARY.next());
+                writer.ws().append("===").ws();
+                context.writeExpr(context.getArgument(1), Precedence.COMPARISON.next());
+                writer.ws().append("?").ws().append("1").ws().append(":").ws().append("0");
+                if (context.getPrecedence().ordinal() >= Precedence.CONDITIONAL.ordinal()) {
+                    writer.append(")");
+                }
+                break;
+            }
+            case "throwCCEIfFalse": {
+                writer.appendFunction("$rt_throwCCEIfFalse").append("(");
+                context.writeExpr(context.getArgument(0), Precedence.min());
+                writer.append(",").ws();
+                context.writeExpr(context.getArgument(1), Precedence.min());
+                writer.append(")");
+                break;
+            }
 
             default:
                 if (methodRef.getName().startsWith("unwrap")) {

jso/impl/src/main/java/org/teavm/jso/impl/JSValueMarshaller.java

@@ -550,7 +550,7 @@ class JSValueMarshaller {
 
     Variable addString(String str, TextLocation location) {
         Variable var = program.createVariable();
-        StringConstantInstruction nameInsn = new StringConstantInstruction();
+        var nameInsn = new StringConstantInstruction();
         nameInsn.setReceiver(var);
         nameInsn.setConstant(str);
         nameInsn.setLocation(location);
@@ -558,6 +558,10 @@ class JSValueMarshaller {
         return var;
     }
 
+    Variable addJsString(String str, TextLocation location) {
+        return addStringWrap(addString(str, location), location);
+    }
+
     Variable classRef(String className, TextLocation location) {
         String name = null;
         String module = null;
@@ -586,16 +590,10 @@ class JSValueMarshaller {
     }
 
     Variable globalRef(String name, TextLocation location) {
-        var nameInsn = new StringConstantInstruction();
-        nameInsn.setReceiver(program.createVariable());
-        nameInsn.setConstant(name);
-        nameInsn.setLocation(location);
-        replacement.add(nameInsn);
-
         var invoke = new InvokeInstruction();
         invoke.setType(InvocationType.SPECIAL);
         invoke.setMethod(JSMethods.GLOBAL);
-        invoke.setArguments(nameInsn.getReceiver());
+        invoke.setArguments(addString(name, location));
         invoke.setReceiver(program.createVariable());
         invoke.setLocation(location);
         replacement.add(invoke);
@@ -618,26 +616,11 @@ class JSValueMarshaller {
         invoke.setLocation(location);
         replacement.add(invoke);
 
-        var nameInsn = new StringConstantInstruction();
-        nameInsn.setReceiver(program.createVariable());
-        nameInsn.setConstant(name);
-        nameInsn.setLocation(location);
-        replacement.add(nameInsn);
-
-        var wrapName = new InvokeInstruction();
-        wrapName.setType(InvocationType.SPECIAL);
-        wrapName.setMethod(referenceCache.getCached(new MethodReference(JS.class, "wrap",
-                String.class, JSObject.class)));
-        wrapName.setReceiver(program.createVariable());
-        wrapName.setArguments(nameInsn.getReceiver());
-        wrapName.setLocation(location);
-        replacement.add(wrapName);
-
         var get = new InvokeInstruction();
         get.setType(InvocationType.SPECIAL);
         get.setMethod(JSMethods.GET_PURE);
         get.setReceiver(program.createVariable());
-        get.setArguments(invoke.getReceiver(), wrapName.getReceiver());
+        get.setArguments(invoke.getReceiver(), addJsString(name, location));
         get.setLocation(location);
         replacement.add(get);
 

jso/impl/src/main/java/org/teavm/jso/impl/JSWrapper.java

@@ -17,6 +17,7 @@ package org.teavm.jso.impl;
 
 import org.teavm.interop.NoSideEffects;
 import org.teavm.jso.JSBody;
+import org.teavm.jso.JSClass;
 import org.teavm.jso.JSObject;
 import org.teavm.jso.core.JSBoolean;
 import org.teavm.jso.core.JSFinalizationRegistry;
@@ -24,11 +25,12 @@ import org.teavm.jso.core.JSMap;
 import org.teavm.jso.core.JSNumber;
 import org.teavm.jso.core.JSObjects;
 import org.teavm.jso.core.JSString;
+import org.teavm.jso.core.JSUndefined;
 import org.teavm.jso.core.JSWeakMap;
 import org.teavm.jso.core.JSWeakRef;
 
 public final class JSWrapper {
-    private static final JSWeakMap<JSObject, JSNumber> hashCodes = new JSWeakMap<>();
+    private static final JSWeakMap<JSObject, JSTransparentInt> hashCodes = new JSWeakMap<>();
     private static final JSWeakMap<JSObject, JSWeakRef<JSObject>> wrappers = JSWeakRef.isSupported()
             ? new JSWeakMap<>() : null;
     private static final JSMap<JSString, JSWeakRef<JSObject>> stringWrappers = JSWeakRef.isSupported()
@@ -68,8 +70,8 @@ public final class JSWrapper {
         if (wrappers != null) {
             if (isObject) {
                 var existingRef = get(wrappers, js);
-                var existing = !JSObjects.isUndefined(existingRef) ? deref(existingRef) : JSObjects.undefined();
+                var existing = !isUndefined(existingRef) ? deref(existingRef) : JSUndefined.instance();
-                if (JSObjects.isUndefined(existing)) {
+                if (isUndefined(existing)) {
                     var wrapper = new JSWrapper(js);
                     set(wrappers, js, createWeakRef(wrapperToJs(wrapper)));
                     return wrapper;
@@ -79,8 +81,8 @@ public final class JSWrapper {
             } else if (type.equals("string")) {
                 var jsString = (JSString) js;
                 var existingRef = get(stringWrappers, jsString);
-                var existing = !JSObjects.isUndefined(existingRef) ? deref(existingRef) : JSObjects.undefined();
+                var existing = !isUndefined(existingRef) ? deref(existingRef) : JSUndefined.instance();
-                if (JSObjects.isUndefined(existing)) {
+                if (isUndefined(existing)) {
                     var wrapper = new JSWrapper(js);
                     var wrapperAsJs = wrapperToJs(wrapper);
                     set(stringWrappers, jsString, createWeakRef(wrapperAsJs));
@@ -92,8 +94,8 @@ public final class JSWrapper {
             } else if (type.equals("number")) {
                 var jsNumber = (JSNumber) js;
                 var existingRef = get(numberWrappers, jsNumber);
-                var existing = !JSObjects.isUndefined(existingRef) ? deref(existingRef) : JSObjects.undefined();
+                var existing = !isUndefined(existingRef) ? deref(existingRef) : JSUndefined.instance();
-                if (JSObjects.isUndefined(existing)) {
+                if (isUndefined(existing)) {
                     var wrapper = new JSWrapper(js);
                     var wrapperAsJs = wrapperToJs(wrapper);
                     set(numberWrappers, jsNumber, createWeakRef(wrapperAsJs));
@@ -104,8 +106,8 @@ public final class JSWrapper {
                 }
             } else if (type.equals("undefined")) {
                 var existingRef = undefinedWrapper;
-                var existing = existingRef != null ? deref(existingRef) : JSObjects.undefined();
+                var existing = existingRef != null ? deref(existingRef) : JSUndefined.instance();
-                if (JSObjects.isUndefined(existing)) {
+                if (isUndefined(existing)) {
                     var wrapper = new JSWrapper(js);
                     var wrapperAsJs = wrapperToJs(wrapper);
                     undefinedWrapper = createWeakRef(wrapperAsJs);
@@ -215,13 +217,21 @@ public final class JSWrapper {
         return !isJava(o) || o instanceof JSWrapper;
     }
 
+    public static boolean isPrimitive(Object o, JSObject primitive) {
+        return isJs(o) && JS.isPrimitive(maybeUnwrap(o), primitive);
+    }
+
+    public static boolean instanceOf(Object o, JSObject type) {
+        return isJs(o) && JS.instanceOf(maybeUnwrap(o), type);
+    }
+
     @Override
     public int hashCode() {
         var type = JSObjects.typeOf(js);
         if (type.equals("object") || type.equals("symbol") || type.equals("function")) {
             var code = hashCodes.get(js);
-            if (JSObjects.isUndefined(code)) {
+            if (isUndefined(code)) {
-                code = JSNumber.valueOf(++hashCodeGen);
+                code = JSTransparentInt.valueOf(++hashCodeGen);
                 hashCodes.set(js, code);
             }
             return code.intValue();
@@ -263,6 +273,18 @@ public final class JSWrapper {
 
     @Override
     public String toString() {
-        return JSObjects.isUndefined(js) ? "undefined" : JSObjects.toString(js);
+        return isUndefined(js) ? "undefined" : JSObjects.toString(js);
     }
+
+    @JSClass(transparent = true)
+    static abstract class JSTransparentInt implements JSObject {
+        @JSBody(script = "return this;")
+        native int intValue();
+
+        @JSBody(params = "value", script = "return value;")
+        static native JSTransparentInt valueOf(int value);
+    }
+
+    @JSBody(params = "obj", script = "return typeof obj == 'undefined'")
+    private static native boolean isUndefined(JSObject obj);
 }

tests/src/test/java/org/teavm/jso/test/InstanceOfTest.java

@@ -0,0 +1,118 @@
+/*
+ *  Copyright 2024 Alexey Andreev.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *       http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.teavm.jso.test;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.teavm.jso.JSBody;
+import org.teavm.jso.JSClass;
+import org.teavm.jso.JSObject;
+import org.teavm.jso.JSProperty;
+import org.teavm.jso.core.JSNumber;
+import org.teavm.junit.AttachJavaScript;
+import org.teavm.junit.EachTestCompiledSeparately;
+import org.teavm.junit.OnlyPlatform;
+import org.teavm.junit.SkipJVM;
+import org.teavm.junit.TeaVMTestRunner;
+import org.teavm.junit.TestPlatform;
+
+@RunWith(TeaVMTestRunner.class)
+@SkipJVM
+@OnlyPlatform(TestPlatform.JAVASCRIPT)
+@EachTestCompiledSeparately
+public class InstanceOfTest {
+    @Test
+    @AttachJavaScript("org/teavm/jso/test/classWithConstructor.js")
+    public void instanceOf() {
+        var a = createClassWithConstructor();
+        assertTrue(a instanceof ClassWithConstructor);
+        assertFalse(a instanceof JSNumber);
+        assertTrue(a instanceof I);
+        assertTrue(a instanceof C);
+
+        var b = callCreateClassWithConstructor();
+        assertTrue(b instanceof ClassWithConstructor);
+        assertFalse(b instanceof JSNumber);
+        assertTrue(b instanceof I);
+        assertTrue(b instanceof C);
+
+        var c = createNumber();
+        assertFalse(c instanceof ClassWithConstructor);
+        assertTrue(c instanceof JSNumber);
+        assertTrue(c instanceof I);
+        assertTrue(c instanceof C);
+
+        var d = callCreateNumber();
+        assertFalse(d instanceof ClassWithConstructor);
+        assertTrue(d instanceof JSNumber);
+        assertTrue(d instanceof I);
+        assertTrue(d instanceof C);
+    }
+
+    @Test
+    @AttachJavaScript("org/teavm/jso/test/classWithConstructor.js")
+    public void cast() {
+        var a = createClassWithConstructor();
+        assertEquals(99, ((ClassWithConstructor) a).getFoo());
+
+        try {
+            assertEquals(99, ((JSNumber) a).intValue());
+            fail("CCE not thrown");
+        } catch (ClassCastException e) {
+            // expected
+        }
+        assertEquals(99, ((I) a).getFoo());
+        assertEquals(99, ((C) a).getFoo());
+
+        var c = createNumber();
+        assertEquals(23, ((JSNumber) c).intValue());
+        try {
+            assertEquals(99, ((ClassWithConstructor) c).getFoo());
+            fail("CCE not thrown");
+        } catch (ClassCastException e) {
+            // expected
+        }
+    }
+
+    private Object callCreateClassWithConstructor() {
+        return createClassWithConstructor();
+    }
+
+    @JSBody(script = "return new ClassWithConstructor();")
+    private static native JSObject createClassWithConstructor();
+
+    private Object callCreateNumber() {
+        return createNumber();
+    }
+
+    @JSBody(script = "return 23;")
+    private static native JSObject createNumber();
+
+    interface I extends JSObject {
+        @JSProperty
+        int getFoo();
+    }
+
+    @JSClass(transparent = true)
+    abstract class C implements JSObject {
+        @JSProperty
+        public abstract int getFoo();
+    }
+}

tests/src/test/java/org/teavm/jso/test/JSWrapperTest.java

@@ -32,6 +32,7 @@ import org.teavm.jso.JSObject;
 import org.teavm.jso.core.JSNumber;
 import org.teavm.jso.core.JSObjects;
 import org.teavm.jso.core.JSString;
+import org.teavm.jso.core.JSUndefined;
 import org.teavm.junit.EachTestCompiledSeparately;
 import org.teavm.junit.OnlyPlatform;
 import org.teavm.junit.SkipJVM;
@@ -313,10 +314,10 @@ public class JSWrapperTest {
 
     @Test
     public void wrapUndefined() {
-        field1 = JSObjects.undefined();
+        field1 = JSUndefined.instance();
         assertEquals("undefined", field1.toString());
-        assertEquals(JSObjects.undefined(), field1);
+        assertEquals(JSUndefined.instance(), field1);
-        assertSame(JSObjects.undefined(), field1);
+        assertSame(JSUndefined.instance(), field1);
         assertTrue(field1 instanceof JSObject);
         assertTrue(JSObjects.isUndefined(field1));
     }