Promises: make null a legal argument for .then

src/promise.js

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 192 matching lines @@
   } catch(e) {
     // TODO(rossberg): perhaps log uncaught exceptions below.
     try { deferred.reject(e) } catch(e) {}
   }
 }
 
 
 // Multi-unwrapped chaining with thenable coercion.
 
 function PromiseThen(onResolve, onReject) {
-  onResolve = IS_UNDEFINED(onResolve) ? PromiseIdResolveHandler : onResolve;
+  onResolve =
+    IS_NULL_OR_UNDEFINED(onResolve) ? PromiseIdResolveHandler : onResolve;
+  onReject =
+    IS_NULL_OR_UNDEFINED(onReject) ? PromiseIdRejectHandler : onReject;
   var that = this;
   var constructor = this.constructor;
   return this.chain(
     function(x) {
       x = PromiseCoerce(constructor, x);
       return x === that ? onReject(MakeTypeError('promise_cyclic', [x])) :
              IsPromise(x) ? x.then(onResolve, onReject) : onResolve(x);
     },
     onReject
   );
 }
 
 PromiseCoerce.table = new $WeakMap;
 
 function PromiseCoerce(constructor, x) {
   if (!IsPromise(x) && IS_SPEC_OBJECT(x)) {
     var then;
     try {
       then = x.then;
-    } catch(e) {
-      var deferred = %_CallFunction(constructor, PromiseDeferred);
-      PromiseCoerce.table.set(x, deferred.promise);
-      deferred.reject(e);
-      return deferred.promise;
+    } catch(r) {

[Sven Panne, 2014/03/18 14:46:18]

Let me guess why you changed this... :-D

[rossberg, 2014/03/18 14:48:20]

Reg-exps are the null pointers of parsing....

+      var promise = %_CallFunction(constructor, r, PromiseRejected);
+      PromiseCoerce.table.set(x, promise);
+      return promise;
     }
     if (typeof then === 'function') {
       if (PromiseCoerce.table.has(x)) {
         return PromiseCoerce.table.get(x);
       } else {
         var deferred = %_CallFunction(constructor, PromiseDeferred);
         PromiseCoerce.table.set(x, deferred.promise);
         try {
           %_CallFunction(x, deferred.resolve, deferred.reject, then);
-        } catch(e) {
-          deferred.reject(e);
+        } catch(r) {
+          deferred.reject(r);
         }
         return deferred.promise;
       }
     }
   }
   return x;
 }
 
 
 // Combinators.
@@ skipping 65 matching lines @@
     "cast", PromiseCast
   ]);
   InstallFunctions($Promise.prototype, DONT_ENUM, [
     "chain", PromiseChain,
     "then", PromiseThen,
     "catch", PromiseCatch
   ]);
 }
 
 SetUpPromise();