[promise] separate PerformPromiseThen from PromiseThen

src/js/promise.js

Index: src/js/promise.js
diff --git a/src/js/promise.js b/src/js/promise.js
index 466912d5eb6eaba98a8e4d9fe41c90ead55c4667..20ffc8c4892327ac68f5242c7900a1006303959e 100644
--- a/src/js/promise.js
+++ b/src/js/promise.js
@@ -390,40 +390,47 @@ function PromiseCreateResolved(x) {
   return %_Call(PromiseResolve, GlobalPromise, x);
 }
 
-// ES#sec-promise.prototype.then
-// Promise.prototype.then ( onFulfilled, onRejected )
-// Multi-unwrapped chaining with thenable coercion.
-function PromiseThen(onResolve, onReject) {
-  var status = GET_PRIVATE(this, promiseStateSymbol);
-  if (IS_UNDEFINED(status)) {
-    throw MakeTypeError(kNotAPromise, this);
-  }
+function PerformPromiseThen(promise, onResolve, onReject, resultCapability) {
+  if (!IS_CALLABLE(onResolve)) onResolve = PromiseIdResolveHandler;
+  if (!IS_CALLABLE(onReject)) onReject = PromiseIdRejectHandler;
 
-  var constructor = SpeciesConstructor(this, GlobalPromise);
-  onResolve = IS_CALLABLE(onResolve) ? onResolve : PromiseIdResolveHandler;
-  onReject = IS_CALLABLE(onReject) ? onReject : PromiseIdRejectHandler;
-  var deferred = NewPromiseCapability(constructor);
+  var status = GET_PRIVATE(promise, promiseStateSymbol);
   switch (status) {
     case kPending:
-      PromiseAttachCallbacks(this, deferred, onResolve, onReject);
+      PromiseAttachCallbacks(promise, resultCapability, onResolve, onReject);
       break;
     case kFulfilled:
-      PromiseEnqueue(GET_PRIVATE(this, promiseResultSymbol),
-                     onResolve, deferred, kFulfilled);
+      PromiseEnqueue(GET_PRIVATE(promise, promiseResultSymbol),
+                     onResolve, resultCapability, kFulfilled);
       break;
     case kRejected:
-      if (!HAS_DEFINED_PRIVATE(this, promiseHasHandlerSymbol)) {
+      if (!HAS_DEFINED_PRIVATE(promise, promiseHasHandlerSymbol)) {
         // Promise has already been rejected, but had no handler.
         // Revoke previously triggered reject event.
-        %PromiseRevokeReject(this);
+        %PromiseRevokeReject(promise);
       }
-      PromiseEnqueue(GET_PRIVATE(this, promiseResultSymbol),
-                     onReject, deferred, kRejected);
+      PromiseEnqueue(GET_PRIVATE(promise, promiseResultSymbol),
+                     onReject, resultCapability, kRejected);
       break;
   }
+
   // Mark this promise as having handler.
-  SET_PRIVATE(this, promiseHasHandlerSymbol, true);
-  return deferred.promise;
+  SET_PRIVATE(promise, promiseHasHandlerSymbol, true);
+  return resultCapability.promise;
+}
+
+// ES#sec-promise.prototype.then
+// Promise.prototype.then ( onFulfilled, onRejected )
+// Multi-unwrapped chaining with thenable coercion.
+function PromiseThen(onResolve, onReject) {
+  var status = GET_PRIVATE(this, promiseStateSymbol);
+  if (IS_UNDEFINED(status)) {
+    throw MakeTypeError(kNotAPromise, this);
+  }
+
+  var constructor = SpeciesConstructor(this, GlobalPromise);
+  var resultCapability = NewPromiseCapability(constructor);
+  return PerformPromiseThen(this, onResolve, onReject, resultCapability);
 }
 
 // Unspecified V8-specific legacy function
@@ -622,6 +629,8 @@ utils.InstallFunctions(extrasUtils, 0, [
     fn => %FunctionRemovePrototype(fn));
 
 utils.Export(function(to) {
+  to.IsPromise = IsPromise;
+
   to.PromiseChain = PromiseChain;
   to.PromiseDefer = PromiseDefer;
   to.PromiseAccept = PromiseAccept;
@@ -629,6 +638,10 @@ utils.Export(function(to) {
   to.PromiseCreateRejected = PromiseCreateRejected;
   to.PromiseCreateResolved = PromiseCreateResolved;
   to.PromiseThen = PromiseThen;
+
+  to.GlobalPromise = GlobalPromise;
+  to.NewPromiseCapability = NewPromiseCapability;
+  to.PerformPromiseThen = PerformPromiseThen;
 });
 
 })