Pass class as this context to custom serializer/deserializer methods

.changeset/shaky-seals-raise.md

@@ -0,0 +1,5 @@
+---
+"@workflow/core": patch
+---
+
+Pass class as `this` context to custom serializer/deserializer methods

packages/core/src/serialization.test.ts

@@ -2217,6 +2217,66 @@ describe('custom class serialization', () => {
     expect(hydrated.created).toBeInstanceOf(Date);
     expect(hydrated.created.toISOString()).toBe('2025-01-01T00:00:00.000Z');
   });
+
+  it('should pass class as this context to WORKFLOW_SERIALIZE and WORKFLOW_DESERIALIZE', () => {
+    // This test verifies that serialize.call(cls, value) and deserialize.call(cls, data)
+    // properly pass the class as `this` context, which is required when the serializer/deserializer
+    // needs to access static properties or methods on the class
+
+    class Counter {
+      // Static property that the serializer uses via `this`
+      static serializedCount = 0;
+      static deserializedCount = 0;
+
+      constructor(public value: number) {}
+
+      static [WORKFLOW_SERIALIZE](this: typeof Counter, instance: Counter) {
+        // biome-ignore lint/complexity/noThisInStatic: intentionally testing `this` context binding
+        this.serializedCount++;
+        // biome-ignore lint/complexity/noThisInStatic: intentionally testing `this` context binding
+        return { value: instance.value, serializedAt: this.serializedCount };
+      }
+
+      static [WORKFLOW_DESERIALIZE](
+        this: typeof Counter,
+        data: { value: number; serializedAt: number }
+      ) {
+        // biome-ignore lint/complexity/noThisInStatic: intentionally testing `this` context binding
+        this.deserializedCount++;
+        return new Counter(data.value);
+      }
+    }
+
+    // The classId is normally generated by the SWC compiler
+    (Counter as any).classId = 'test/Counter';
+
+    // Register the class for serialization/deserialization
+    registerSerializationClass('test/Counter', Counter);
+
+    // Reset counters
+    Counter.serializedCount = 0;
+    Counter.deserializedCount = 0;
+
+    // Serialize an instance - this should increment serializedCount via `this`
+    const counter = new Counter(42);
+    const serialized = dehydrateWorkflowArguments(counter, [], mockRunId);
+
+    // Verify serialization used `this` correctly
+    expect(Counter.serializedCount).toBe(1);
+
+    // Deserialize - this should increment deserializedCount via `this`
+    const hydrated = hydrateWorkflowArguments(serialized, globalThis);
+
+    // Verify deserialization used `this` correctly
+    expect(Counter.deserializedCount).toBe(1);
+    expect(hydrated).toBeInstanceOf(Counter);
+    expect(hydrated.value).toBe(42);
+
+    // Serialize another instance to verify counter increments
+    const counter2 = new Counter(100);
+    dehydrateWorkflowArguments(counter2, [], mockRunId);
+    expect(Counter.serializedCount).toBe(2);
+  });
 });
 
 describe('format prefix system', () => {

packages/core/src/serialization.ts

@@ -551,25 +551,25 @@ function getCommonReducers(global: Record<string, any> = globalThis) {
     Instance: (value) => {
       // Check if this is an instance of a class with custom serialization
       if (value === null || typeof value !== 'object') return false;
-      const ctor = value.constructor;
-      if (!ctor || typeof ctor !== 'function') return false;
+      const cls = value.constructor;
+      if (!cls || typeof cls !== 'function') return false;
 
       // Check if the class has a static WORKFLOW_SERIALIZE method
-      const serialize = ctor[WORKFLOW_SERIALIZE];
+      const serialize = cls[WORKFLOW_SERIALIZE];
       if (typeof serialize !== 'function') {
         return false;
       }
 
       // Get the classId from the static class property (set by SWC plugin)
-      const classId = ctor.classId;
+      const classId = cls.classId;
       if (typeof classId !== 'string') {
         throw new Error(
-          `Class "${ctor.name}" with ${String(WORKFLOW_SERIALIZE)} must have a static "classId" property.`
+          `Class "${cls.name}" with ${String(WORKFLOW_SERIALIZE)} must have a static "classId" property.`
         );
       }
 
       // Serialize the instance using the custom serializer
-      const data = serialize(value);
+      const data = serialize.call(cls, value);
       return { classId, data };
     },
     Set: (value) => value instanceof global.Set && Array.from(value),
@@ -890,7 +890,7 @@ export function getCommonRevivers(global: Record<string, any> = globalThis) {
       }
 
       // Deserialize the instance using the custom deserializer
-      return deserialize(data);
+      return deserialize.call(cls, data);
     },
     Set: (value) => new global.Set(value),
     StepFunction: (value) => {