Add then and catch methods to Promise class

doc/promises.md

@@ -75,5 +75,47 @@ Rejects the Promise object held by the `Napi::Promise::Deferred` object.
 
 * `[in] value`: The Node-API primitive value with which to reject the `Napi::Promise`.
 
+## Promise Methods
+
+### Then
+
+```cpp
+<Promise> Napi::Promise::Then(napi_value onFulfilled, napi_value onRejected) const;
+```
+
+Attaches fulfillment and/or rejection handlers to the promise and returns a new promise.
+
+**Parameters:**
+* `[in] onFulfilled`: A function to be called when the promise is fulfilled
+* `[in] onRejected`: A function to be called when the promise is rejected (optional)
+
+**Returns:** A new `<Promise>` that resolves or rejects based on the handler's result.
+
+**Example:**
+```cpp
+// Single fulfillment handler
+Promise newPromise = existingPromise.Then(fulfillmentHandler);
+
+// Both fulfillment and rejection handlers
+Promise chainedPromise = existingPromise.Then(onFulfilled, onRejected);
+```
+
+### Catch
+
+```cpp
+<Promise> Napi::Promise::Catch(napi_value onRejected) const;
+```
+
+Attaches a rejection handler to the promise and returns a new promise.
+
+**Parameters:**
+* `[in] onRejected`: A function to be called when the promise is rejected
+
+**Returns:** A new `<Promise>` that handles rejection cases.
+
+**Example:**
+```cpp
+Promise handledPromise = existingPromise.Catch(rejectionHandler);
+```
 
 [`Napi::Object`]: ./object.md

napi-inl.h

@@ -2813,6 +2813,78 @@ inline void Promise::CheckCast(napi_env env, napi_value value) {
 
 inline Promise::Promise(napi_env env, napi_value value) : Object(env, value) {}
 
+inline MaybeOrValue<Promise> Promise::Then(napi_value onFulfilled) const {
+  EscapableHandleScope scope(_env);
+#ifdef NODE_ADDON_API_ENABLE_MAYBE
+  MaybeOrValue<Value> thenMethodMaybe = Get("then");
+  Function thenMethod = thenMethodMaybe.Unwrap().As<Function>();
+  MaybeOrValue<Value> result = thenMethod.Call(*this, {onFulfilled});
+  if (result.IsJust()) {
+    return Just(scope.Escape(result.Unwrap()).As<Promise>());
+  }
+  return Nothing<Promise>();
+#else
+  Function thenMethod = Get("then").As<Function>();
+  MaybeOrValue<Value> result = thenMethod.Call(*this, {onFulfilled});
+  if (scope.Env().IsExceptionPending()) {
+    return Promise();
+  }
+  return scope.Escape(result).As<Promise>();
+#endif
+}
+
+inline MaybeOrValue<Promise> Promise::Then(napi_value onFulfilled, napi_value onRejected) const {
+  EscapableHandleScope scope(_env);
+#ifdef NODE_ADDON_API_ENABLE_MAYBE
+  MaybeOrValue<Value> thenMethodMaybe = Get("then");
+  Function thenMethod = thenMethodMaybe.Unwrap().As<Function>();
+  MaybeOrValue<Value> result = thenMethod.Call(*this, {onFulfilled, onRejected});
+  if (result.IsJust()) {
+    return Just(scope.Escape(result.Unwrap()).As<Promise>());
+  }
+  return Nothing<Promise>();
+#else
+  Function thenMethod = Get("then").As<Function>();
+  MaybeOrValue<Value> result = thenMethod.Call(*this, {onFulfilled, onRejected});
+  if (scope.Env().IsExceptionPending()) {
+    return Promise();
+  }
+  return scope.Escape(result).As<Promise>();
+#endif
+}
+
+inline MaybeOrValue<Promise> Promise::Catch(napi_value onRejected) const {
+  EscapableHandleScope scope(_env);
+#ifdef NODE_ADDON_API_ENABLE_MAYBE
+  MaybeOrValue<Value> catchMethodMaybe = Get("catch");
+  Function catchMethod = catchMethodMaybe.Unwrap().As<Function>();
+  MaybeOrValue<Value> result = catchMethod.Call(*this, {onRejected});
+  if (result.IsJust()) {
+    return Just(scope.Escape(result.Unwrap()).As<Promise>());
+  }
+  return Nothing<Promise>();
+#else
+  Function catchMethod = Get("catch").As<Function>();
+  MaybeOrValue<Value> result = catchMethod.Call(*this, {onRejected});
+  if (scope.Env().IsExceptionPending()) {
+    return Promise();
+  }
+  return scope.Escape(result).As<Promise>();
+#endif
+}
+
+inline MaybeOrValue<Promise> Promise::Then(const Function& onFulfilled) const {
+  return Then(static_cast<napi_value>(onFulfilled));
+}
+
+inline MaybeOrValue<Promise> Promise::Then(const Function& onFulfilled, const Function& onRejected) const {
+  return Then(static_cast<napi_value>(onFulfilled), static_cast<napi_value>(onRejected));
+}
+
+inline MaybeOrValue<Promise> Promise::Catch(const Function& onRejected) const {
+  return Catch(static_cast<napi_value>(onRejected));
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // Buffer<T> class
 ////////////////////////////////////////////////////////////////////////////////

napi.h

@@ -1574,7 +1574,16 @@ class Promise : public Object {
 
   static void CheckCast(napi_env env, napi_value value);
 
+  Promise();
   Promise(napi_env env, napi_value value);
+
+  MaybeOrValue<Promise> Then(napi_value onFulfilled) const;
+  MaybeOrValue<Promise> Then(napi_value onFulfilled, napi_value onRejected) const;
+  MaybeOrValue<Promise> Catch(napi_value onRejected) const;
+
+  MaybeOrValue<Promise> Then(const Function& onFulfilled) const;
+  MaybeOrValue<Promise> Then(const Function& onFulfilled, const Function& onRejected) const;
+  MaybeOrValue<Promise> Catch(const Function& onRejected) const;
 };
 
 template <typename T>

test/promise.cc

@@ -1,4 +1,5 @@
 #include "napi.h"
+#include "test_helper.h"
 
 using namespace Napi;
 
@@ -23,6 +24,72 @@ Value PromiseReturnsCorrectEnv(const CallbackInfo& info) {
   return Boolean::New(info.Env(), deferred.Env() == info.Env());
 }
 
+Value ThenMethodOnFulfilled(const CallbackInfo& info) {
+  auto deferred = Promise::Deferred::New(info.Env());
+  Function onFulfilled = info[0].As<Function>();
+
+  Promise resultPromise = MaybeUnwrap(deferred.Promise().Then(onFulfilled));
+
+  bool isPromise = resultPromise.IsPromise();
+  deferred.Resolve(Number::New(info.Env(), 42));
+
+  Object result = Object::New(info.Env());
+  result["isPromise"] = Boolean::New(info.Env(), isPromise);
+  result["promise"] = resultPromise;
+
+  return result;
+}
+
+Value ThenMethodOnFulfilledOnRejectedResolve(const CallbackInfo& info) {
+  auto deferred = Promise::Deferred::New(info.Env());
+  Function onFulfilled = info[0].As<Function>();
+  Function onRejected = info[1].As<Function>();
+
+  Promise resultPromise = MaybeUnwrap(deferred.Promise().Then(onFulfilled, onRejected));
+
+  bool isPromise = resultPromise.IsPromise();
+  deferred.Resolve(Number::New(info.Env(), 42));
+
+  Object result = Object::New(info.Env());
+  result["isPromise"] = Boolean::New(info.Env(), isPromise);
+  result["promise"] = resultPromise;
+
+  return result;
+}
+
+Value ThenMethodOnFulfilledOnRejectedReject(const CallbackInfo& info) {
+  auto deferred = Promise::Deferred::New(info.Env());
+  Function onFulfilled = info[0].As<Function>();
+  Function onRejected = info[1].As<Function>();
+
+  Promise resultPromise = MaybeUnwrap(deferred.Promise().Then(onFulfilled, onRejected));
+
+  bool isPromise = resultPromise.IsPromise();
+  deferred.Reject(String::New(info.Env(), "Rejected"));
+
+  Object result = Object::New(info.Env());
+  result["isPromise"] = Boolean::New(info.Env(), isPromise);
+  result["promise"] = resultPromise;
+
+  return result;
+}
+
+Value CatchMethod(const CallbackInfo& info) {
+  auto deferred = Promise::Deferred::New(info.Env());
+  Function onRejected = info[0].As<Function>();
+
+  Promise resultPromise = MaybeUnwrap(deferred.Promise().Catch(onRejected));
+
+  bool isPromise = resultPromise.IsPromise();
+  deferred.Reject(String::New(info.Env(), "Rejected"));
+
+  Object result = Object::New(info.Env());
+  result["isPromise"] = Boolean::New(info.Env(), isPromise);
+  result["promise"] = resultPromise;
+
+  return result;
+}
+
 Object InitPromise(Env env) {
   Object exports = Object::New(env);
 
@@ -31,6 +98,12 @@ Object InitPromise(Env env) {
   exports["rejectPromise"] = Function::New(env, RejectPromise);
   exports["promiseReturnsCorrectEnv"] =
       Function::New(env, PromiseReturnsCorrectEnv);
+  exports["thenMethodOnFulfilled"] = Function::New(env, ThenMethodOnFulfilled);
+  exports["thenMethodOnFulfilledOnRejectedResolve"] =
+      Function::New(env, ThenMethodOnFulfilledOnRejectedResolve);
+  exports["thenMethodOnFulfilledOnRejectedReject"] =
+      Function::New(env, ThenMethodOnFulfilledOnRejectedReject);
+  exports["catchMethod"] = Function::New(env, CatchMethod);
 
   return exports;
 }

test/promise.js

@@ -17,4 +17,27 @@ async function test (binding) {
   rejecting.then(common.mustNotCall()).catch(common.mustCall());
 
   assert(binding.promise.promiseReturnsCorrectEnv());
+
+  const onFulfilled = (value) => value * 2;
+  const onRejected = (reason) => reason + '!';
+
+  const thenOnFulfilled = binding.promise.thenMethodOnFulfilled(onFulfilled);
+  assert.strictEqual(thenOnFulfilled.isPromise, true);
+  const onFulfilledValue = await thenOnFulfilled.promise;
+  assert.strictEqual(onFulfilledValue, 84);
+
+  const thenResolve = binding.promise.thenMethodOnFulfilledOnRejectedResolve(onFulfilled, onRejected);
+  assert.strictEqual(thenResolve.isPromise, true);
+  const thenResolveValue = await thenResolve.promise;
+  assert.strictEqual(thenResolveValue, 84);
+
+  const thenRejected = binding.promise.thenMethodOnFulfilledOnRejectedReject(onFulfilled, onRejected);
+  assert.strictEqual(thenRejected.isPromise, true);
+  const rejectedValue = await thenRejected.promise;
+  assert.strictEqual(rejectedValue, 'Rejected!');
+
+  const catchMethod = binding.promise.catchMethod(onRejected);
+  assert.strictEqual(catchMethod.isPromise, true);
+  const catchValue = await catchMethod.promise;
+  assert.strictEqual(catchValue, 'Rejected!');
 }