fix #3412 (#3422)

2 files changed, 22 insertions, 4 deletions

diff --git a/src/bun.js/bindings/JSMockFunction.cpp b/src/bun.js/bindings/JSMockFunction.cpp
index fbfcf0c9e..33922c2b7 100644
--- a/src/bun.js/bindings/JSMockFunction.cpp
+++ b/src/bun.js/bindings/JSMockFunction.cpp
@@ -569,15 +569,19 @@ extern "C" EncodedJSValue JSMock__jsSpyOn(JSC::JSGlobalObject* lexicalGlobalObje
 
     // easymode: regular property or missing property
     if (!hasValue || slot.isValue()) {
+        JSValue value = jsUndefined();
+        if (hasValue) {
+            value = slot.getValue(globalObject, propertyKey);
+            if (jsDynamicCast<JSMockFunction*>(value)) {
+                return JSValue::encode(value);
+            }
+        }
+
         auto* mock = JSMockFunction::create(vm, globalObject, globalObject->mockModule.mockFunctionStructure.getInitializedOnMainThread(globalObject), CallbackKind::GetterSetter);
         mock->spyTarget = JSC::Weak<JSObject>(object, &weakValueHandleOwner(), nullptr);
         mock->spyIdentifier = propertyKey.isSymbol() ? Identifier::fromUid(vm, propertyKey.uid()) : Identifier::fromString(vm, propertyKey.publicName());
         mock->spyAttributes = hasValue ? slot.attributes() : 0;
         unsigned attributes = 0;
-        JSValue value = jsUndefined();
-
-        if (hasValue)
-            value = slot.getValue(globalObject, propertyKey);
 
         if (hasValue && ((slot.attributes() & PropertyAttribute::Function) != 0 || (value.isCell() && value.isCallable()))) {
             if (hasValue)
diff --git a/test/js/bun/test/mock-fn.test.js b/test/js/bun/test/mock-fn.test.js
index 8504e3d70..ef3c4b7d3 100644
--- a/test/js/bun/test/mock-fn.test.js
+++ b/test/js/bun/test/mock-fn.test.js
@@ -603,5 +603,19 @@ describe("spyOn", () => {
     });
   }
 
+  test("spyOn twice works", () => {
+    var obj = {
+      original() {
+        return 42;
+      },
+    };
+    const _original = obj.original;
+    const fn = spyOn(obj, "original");
+    const fn2 = spyOn(obj, "original");
+    expect(fn).toBe(obj.original);
+    expect(fn2).toBe(fn);
+    expect(fn).not.toBe(_original);
+  });
+
   // spyOn does not work with getters/setters yet.
 });