diff --git a/IntegrationTests/TestSuites/Sources/PrimaryTests/main.swift b/IntegrationTests/TestSuites/Sources/PrimaryTests/main.swift
index b58b037e7..140cc0bd3 100644
--- a/IntegrationTests/TestSuites/Sources/PrimaryTests/main.swift
+++ b/IntegrationTests/TestSuites/Sources/PrimaryTests/main.swift
@@ -228,6 +228,8 @@ New_Object_Construction: do {
     let cat1 = objectConstructor.new("Tama", 3, true)
     try expectEqual(getJSValue(this: cat1, name: "name"), .string("Tama"))
     try expectEqual(getJSValue(this: cat1, name: "age"), .number(3))
+    try expectEqual(cat1.instanceof(objectConstructor), true)
+    try expectEqual(cat1.instanceof(try expectFunction(getJSValue(this: .global, name: "Array"))), false)
     let cat1Bark = try expectFunction(getJSValue(this: cat1, name: "bark"))
     try expectEqual(cat1Bark(), .string("nyan"))
 
diff --git a/Runtime/src/index.ts b/Runtime/src/index.ts
index b126b3e4f..94e436aed 100644
--- a/Runtime/src/index.ts
+++ b/Runtime/src/index.ts
@@ -59,7 +59,7 @@ class SwiftRuntimeHeap {
 
     allocHeap(value: any) {
         const isObject = typeof value == "object";
-        const entry = this._heapEntryByValue.get(value); 
+        const entry = this._heapEntryByValue.get(value);
         if (isObject && entry) {
             entry.rc++
             return entry.id
@@ -362,6 +362,14 @@ export class SwiftRuntime {
                     throw Error(`Invalid result type of object constructor of "${obj}": "${result}"`)
                 writeUint32(result_obj, this.heap.allocHeap(result));
             },
+            swjs_instanceof: (
+                obj_ref: ref, constructor_ref: ref,
+                result_ptr: pointer
+            ) => {
+              const obj = this.heap.referenceHeap(obj_ref)
+              const constructor = this.heap.referenceHeap(constructor_ref)
+              return obj instanceof constructor
+            },
             swjs_destroy_ref: (ref: ref) => {
                 this.heap.freeHeap(ref)
             }
diff --git a/Sources/JavaScriptKit/JSObject.swift b/Sources/JavaScriptKit/JSObject.swift
index 2253d9775..47ae2b4a6 100644
--- a/Sources/JavaScriptKit/JSObject.swift
+++ b/Sources/JavaScriptKit/JSObject.swift
@@ -32,6 +32,10 @@ public class JSObjectRef: Equatable {
         getJSValue(this: self, index: Int32(index))
     }
 
+    public func instanceof(_ constructor: JSFunctionRef) -> Bool {
+        _instanceof(self.id, constructor.id)
+    }
+
     public subscript(_ index: Int) -> JSValue {
         get { get(index) }
         set { set(index, newValue) }
diff --git a/Sources/JavaScriptKit/XcodeSupport.swift b/Sources/JavaScriptKit/XcodeSupport.swift
index b75972444..180072ebf 100644
--- a/Sources/JavaScriptKit/XcodeSupport.swift
+++ b/Sources/JavaScriptKit/XcodeSupport.swift
@@ -64,6 +64,10 @@ import _CJavaScriptKit
         _: UnsafePointer<RawJSValue>!, _: Int32,
         _: UnsafeMutablePointer<JavaScriptObjectRef>!
     ) { fatalError() }
+    func _instanceof(
+        _: JavaScriptObjectRef,
+      _: JavaScriptObjectRef
+    ) -> Bool { fatalError() }
     func _create_function(
         _: JavaScriptHostFuncRef,
         _: UnsafePointer<JavaScriptObjectRef>!
diff --git a/Sources/_CJavaScriptKit/include/_CJavaScriptKit.h b/Sources/_CJavaScriptKit/include/_CJavaScriptKit.h
index bc54ba345..61789e16c 100644
--- a/Sources/_CJavaScriptKit/include/_CJavaScriptKit.h
+++ b/Sources/_CJavaScriptKit/include/_CJavaScriptKit.h
@@ -2,6 +2,7 @@
 #define _CJavaScriptKit_h
 
 #include <stdlib.h>
+#include <stdbool.h>
 
 typedef unsigned int JavaScriptObjectRef;
 typedef unsigned int JavaScriptHostFuncRef;
@@ -82,6 +83,11 @@ __attribute__((__import_module__("javascript_kit"),
 _call_new(const JavaScriptObjectRef ref, const RawJSValue *argv, const int argc,
           JavaScriptObjectRef *result_obj);
 
+__attribute__((__import_module__("javascript_kit"),
+               __import_name__("swjs_instanceof"))) extern bool
+_instanceof(const JavaScriptObjectRef obj,
+            const JavaScriptObjectRef constructor);
+
 __attribute__((__import_module__("javascript_kit"),
                __import_name__("swjs_create_function"))) extern void
 _create_function(const JavaScriptHostFuncRef host_func_id,