behavior of .next, .return, .throw methods on AsyncIterator helpers proxy iterators aligned with the current spec draft (built-in async generators) (mainly - some early errors moved to returned promises)

Author: zloirock

CHANGELOG.md

@@ -1,7 +1,8 @@
 ## Changelog
 ##### Unreleased
 - `AsyncFromSyncIterator` made stricter, related mainly to `AsyncIterator.from` and `AsyncIterator.prototype.flatMap`
-- Handling of optional `.next` arguments in `(Async)Iterator` methods is aligned with the current spec draft (mainly - ignoring of the first passed to `.next` arguments in built-in generators)
+- Handling of optional `.next` arguments in `(Async)Iterator` methods is aligned with the current spec draft (mainly - ignoring the first passed to `.next` argument in built-in generators)
+- Behavior of `.next`, `.return`, `.throw` methods on `AsyncIterator` helpers proxy iterators aligned with the current spec draft (built-in async generators) (mainly - some early errors moved to returned promises)
 
 ##### 3.16.3 - 2021.08.25
 - Fixed `CreateAsyncFromSyncIterator` semantic in `AsyncIterator.from`, related to [#765](https://github.com/zloirock/core-js/issues/765)

packages/core-js/internals/async-iterator-create-proxy.js

@@ -16,22 +16,6 @@ var getInternalState = InternalStateModule.get;
 
 var TO_STRING_TAG = wellKnownSymbol('toStringTag');
 
-var $return = function (value) {
-  var iterator = getInternalState(this).iterator;
-  var $$return = iterator['return'];
-  return $$return === undefined
-    ? Promise.resolve({ done: true, value: value })
-    : anObject($$return.call(iterator, value));
-};
-
-var $throw = function (value) {
-  var iterator = getInternalState(this).iterator;
-  var $$throw = iterator['throw'];
-  return $$throw === undefined
-    ? Promise.reject(value)
-    : $$throw.call(iterator, value);
-};
-
 module.exports = function (nextHandler, IS_ITERATOR) {
   var AsyncIteratorProxy = function AsyncIterator(state) {
     state.next = aFunction(state.iterator.next);
@@ -45,15 +29,28 @@ module.exports = function (nextHandler, IS_ITERATOR) {
       var state = getInternalState(this);
       var args = arguments.length ? [state.ignoreArg ? undefined : arg] : IS_ITERATOR ? [] : [undefined];
       state.ignoreArg = false;
-      if (state.done) return Promise.resolve({ done: true, value: undefined });
-      try {
-        return Promise.resolve(anObject(nextHandler.call(state, Promise, args)));
-      } catch (error) {
-        return Promise.reject(error);
-      }
+      return new Promise(function (resolve) {
+        resolve(state.done ? { done: true, value: undefined } : anObject(nextHandler.call(state, Promise, args)));
+      });
+    },
+    'return': function (value) {
+      var iterator = getInternalState(this).iterator;
+      return new Promise(function (resolve, reject) {
+        var $$return = iterator['return'];
+        if ($$return === undefined) return resolve({ done: true, value: value });
+        Promise.resolve(anObject($$return.call(iterator, value)).value).then(function (result) {
+          resolve({ done: true, value: result });
+        }, reject);
+      });
     },
-    'return': $return,
-    'throw': $throw
+    'throw': function (value) {
+      var iterator = getInternalState(this).iterator;
+      return new Promise(function (resolve, reject) {
+        var $$throw = iterator['throw'];
+        if ($$throw === undefined) return reject(value);
+        resolve($$throw.call(iterator, value));
+      });
+    }
   });
 
   if (!IS_ITERATOR) {

packages/core-js/internals/iterator-create-proxy.js

@@ -13,19 +13,6 @@ var getInternalState = InternalStateModule.get;
 
 var TO_STRING_TAG = wellKnownSymbol('toStringTag');
 
-var $return = function (value) {
-  var iterator = getInternalState(this).iterator;
-  var $$return = iterator['return'];
-  return $$return === undefined ? { done: true, value: value } : anObject($$return.call(iterator, value));
-};
-
-var $throw = function (value) {
-  var iterator = getInternalState(this).iterator;
-  var $$throw = iterator['throw'];
-  if ($$throw === undefined) throw value;
-  return $$throw.call(iterator, value);
-};
-
 module.exports = function (nextHandler, IS_ITERATOR) {
   var IteratorProxy = function Iterator(state) {
     state.next = aFunction(state.iterator.next);
@@ -42,8 +29,17 @@ module.exports = function (nextHandler, IS_ITERATOR) {
       var result = state.done ? undefined : nextHandler.call(state, args);
       return { done: state.done, value: result };
     },
-    'return': $return,
-    'throw': $throw
+    'return': function (value) {
+      var iterator = getInternalState(this).iterator;
+      var $$return = iterator['return'];
+      return { done: true, value: $$return === undefined ? value : anObject($$return.call(iterator, value)).value };
+    },
+    'throw': function (value) {
+      var iterator = getInternalState(this).iterator;
+      var $$throw = iterator['throw'];
+      if ($$throw === undefined) throw value;
+      return $$throw.call(iterator, value);
+    }
   });
 
   if (!IS_ITERATOR) {