[JS IR BE] Fix overriding property of Throwable

js/js.tests/test/org/jetbrains/kotlin/js/test/ir/semantics/IrBoxJsTestGenerated.java

@@ -2697,6 +2697,11 @@ public class IrBoxJsTestGenerated extends AbstractIrBoxJsTest {
                 runTest("js/js.translator/testData/box/expression/try/nestedTryCatchInCatch.kt");
             }
 
+            @TestMetadata("overrideThrowableProperties.kt")
+            public void testOverrideThrowableProperties() throws Exception {
+                runTest("js/js.translator/testData/box/expression/try/overrideThrowableProperties.kt");
+            }
+
             @TestMetadata("rethrowExceptionIfNotCaught.kt")
             public void testRethrowExceptionIfNotCaught() throws Exception {
                 runTest("js/js.translator/testData/box/expression/try/rethrowExceptionIfNotCaught.kt");

js/js.tests/test/org/jetbrains/kotlin/js/test/semantics/BoxJsTestGenerated.java

@@ -2712,6 +2712,11 @@ public class BoxJsTestGenerated extends AbstractBoxJsTest {
                 runTest("js/js.translator/testData/box/expression/try/nestedTryCatchInCatch.kt");
             }
 
+            @TestMetadata("overrideThrowableProperties.kt")
+            public void testOverrideThrowableProperties() throws Exception {
+                runTest("js/js.translator/testData/box/expression/try/overrideThrowableProperties.kt");
+            }
+
             @TestMetadata("rethrowExceptionIfNotCaught.kt")
             public void testRethrowExceptionIfNotCaught() throws Exception {
                 runTest("js/js.translator/testData/box/expression/try/rethrowExceptionIfNotCaught.kt");

js/js.translator/testData/box/expression/try/overrideThrowableProperties.kt

@@ -0,0 +1,21 @@
+// EXPECTED_REACHABLE_NODES: 1315
+
+open class Ex0(msg: String, cs: Throwable): Throwable(msg, cs)
+
+class Ex1: Ex0("A", Error("fail2")) {
+    override val cause = Error("B")
+}
+
+class Ex2: Ex0("fail3", Error("C")) {
+    override val message = "D"
+}
+
+fun box(): String {
+    val ex1: Throwable = Ex1()
+    val ex2: Throwable = Ex2()
+
+    val r = ex1.message + ex1.cause?.message + ex2.cause?.message + ex2.message
+    if (r != "ABCD") return "Fail: $r"
+
+    return "OK"
+}

libraries/stdlib/js-ir/runtime/coreRuntime.kt

@@ -38,6 +38,10 @@ fun toString(o: dynamic): String = when {
 
 fun anyToString(o: dynamic): String = js("Object").prototype.toString.call(o)
 
+private fun hasOwnPrototypeProperty(o: Any, name: String): Boolean {
+    return JsObject.getPrototypeOf(o).hasOwnProperty(name).unsafeCast<Boolean>()
+}
+
 fun hashCode(obj: dynamic): Int {
     if (obj == null)
         return 0
@@ -95,8 +99,12 @@ internal fun newThrowable(message: String?, cause: Throwable?): Throwable {
 
 internal fun extendThrowable(this_: dynamic, message: String?, cause: Throwable?) {
     js("Error").call(this_)
-    this_.message = message ?: cause?.toString() ?: undefined
+    if (!hasOwnPrototypeProperty(this_, "message")) {
-    this_.cause = cause
+        this_.message = message ?: cause?.toString() ?: undefined
+    }
+    if (!hasOwnPrototypeProperty(this_, "cause")) {
+        this_.cause = cause
+    }
     this_.name = JsObject.getPrototypeOf(this_).constructor.name
     captureStack(this_)
 }