PromiseThen should ignore non-function parameters.

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 130 matching lines @@
   }
 }
 
 
 // Simple chaining.
 
 function PromiseIdResolveHandler(x) { return x }
 function PromiseIdRejectHandler(r) { throw r }
 
 function PromiseChain(onResolve, onReject) {  // a.k.a.  flatMap
-  onResolve = IS_UNDEFINED(onResolve) ? PromiseIdResolveHandler : onResolve;
-  onReject = IS_UNDEFINED(onReject) ? PromiseIdRejectHandler : onReject;
+  onResolve =
+    typeof onResolve === 'function' ? onResolve : PromiseIdResolveHandler;

[rossberg, 2014/04/28 08:32:52]

We shouldn't change .chain, only .then

[yhirano, 2014/04/28 12:35:40]

Done.

+  onReject = typeof onReject === 'function' ? onReject : PromiseIdRejectHandler;
   var deferred = %_CallFunction(this.constructor, PromiseDeferred);
   switch (GET_PRIVATE(this, promiseStatus)) {
     case UNDEFINED:
       throw MakeTypeError('not_a_promise', [this]);
     case 0:  // Pending
       GET_PRIVATE(this, promiseOnResolve).push(onResolve, deferred);
       GET_PRIVATE(this, promiseOnReject).push(onReject, deferred);
       break;
     case +1:  // Resolved
       PromiseEnqueue(GET_PRIVATE(this, promiseValue), [onResolve, deferred]);
@@ skipping 31 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 =
+    typeof onResolve === 'function' ? onResolve : PromiseIdResolveHandler;

[rossberg, 2014/04/28 08:32:52]

Please use the IS_SPEC_FUNCTION macro instead.

[yhirano, 2014/04/28 12:35:40]

Done.

   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
   );
@@ skipping 84 matching lines @@
     "cast", PromiseCast
   ]);
   InstallFunctions($Promise.prototype, DONT_ENUM, [
     "chain", PromiseChain,
     "then", PromiseThen,
     "catch", PromiseCatch
   ]);
 }
 
 SetUpPromise();