native promise-based APIs Promise#{ catch, finally } returns polyfilled Promise instances when it's required

Author: zloirock

CHANGELOG.md

@@ -1,6 +1,6 @@
 ## Changelog
 ##### Unreleased
-- Nothing
+- Native promise-based APIs `Promise#{ catch, finally }` returns polyfilled `Promise` instances when it's required
 
 ##### 3.11.2 - 2021.05.03
 - Added a workaround of WebKit ~ iOS 10.3 Safari `Promise` bug, [#932](https://github.com/zloirock/core-js/issues/932)

packages/core-js/modules/es.promise.finally.js

@@ -30,7 +30,10 @@ $({ target: 'Promise', proto: true, real: true, forced: NON_GENERIC }, {
   }
 });
 
-// patch native Promise.prototype for native async functions
-if (!IS_PURE && typeof NativePromise == 'function' && !NativePromise.prototype['finally']) {
-  redefine(NativePromise.prototype, 'finally', getBuiltIn('Promise').prototype['finally']);
+// makes sure that native promise-based APIs `Promise#finally` properly works with patched `Promise#then`
+if (!IS_PURE && typeof NativePromise == 'function') {
+  var method = getBuiltIn('Promise').prototype['finally'];
+  if (NativePromise.prototype['finally'] !== method) {
+    redefine(NativePromise.prototype, 'finally', method, { unsafe: true });
+  }
 }

packages/core-js/modules/es.promise.js

@@ -36,6 +36,7 @@ var setInternalState = InternalStateModule.set;
 var getInternalPromiseState = InternalStateModule.getterFor(PROMISE);
 var NativePromisePrototype = NativePromise && NativePromise.prototype;
 var PromiseConstructor = NativePromise;
+var PromiseConstructorPrototype = NativePromisePrototype;
 var TypeError = global.TypeError;
 var document = global.document;
 var process = global.process;
@@ -60,7 +61,7 @@ var FORCED = isForced(PROMISE, function () {
   // We can't detect it synchronously, so just check versions
   if (!GLOBAL_CORE_JS_PROMISE && V8_VERSION === 66) return true;
   // We need Promise#finally in the pure version for preventing prototype pollution
-  if (IS_PURE && !PromiseConstructor.prototype['finally']) return true;
+  if (IS_PURE && !PromiseConstructorPrototype['finally']) return true;
   // We can't use @@species feature detection in V8 since it causes
   // deoptimization and performance degradation
   // https://github.com/zloirock/core-js/issues/679
@@ -239,6 +240,7 @@ if (FORCED) {
       internalReject(state, error);
     }
   };
+  PromiseConstructorPrototype = PromiseConstructor.prototype;
   // eslint-disable-next-line no-unused-vars -- required for `.length`
   Internal = function Promise(executor) {
     setInternalState(this, {
@@ -252,7 +254,7 @@ if (FORCED) {
       value: undefined
     });
   };
-  Internal.prototype = redefineAll(PromiseConstructor.prototype, {
+  Internal.prototype = redefineAll(PromiseConstructorPrototype, {
     // `Promise.prototype.then` method
     // https://tc39.es/ecma262/#sec-promise.prototype.then
     then: function then(onFulfilled, onRejected) {
@@ -288,14 +290,19 @@ if (FORCED) {
   if (!IS_PURE && typeof NativePromise == 'function' && NativePromisePrototype !== Object.prototype) {
     nativeThen = NativePromisePrototype.then;
 
-    // make `Promise#then` return a polyfilled `Promise` for native promise-based APIs
-    if (!SUBCLASSING) redefine(NativePromisePrototype, 'then', function then(onFulfilled, onRejected) {
-      var that = this;
-      return new PromiseConstructor(function (resolve, reject) {
-        nativeThen.call(that, resolve, reject);
-      }).then(onFulfilled, onRejected);
-    // https://github.com/zloirock/core-js/issues/640
-    }, { unsafe: true });
+    if (!SUBCLASSING) {
+      // make `Promise#then` return a polyfilled `Promise` for native promise-based APIs
+      redefine(NativePromisePrototype, 'then', function then(onFulfilled, onRejected) {
+        var that = this;
+        return new PromiseConstructor(function (resolve, reject) {
+          nativeThen.call(that, resolve, reject);
+        }).then(onFulfilled, onRejected);
+      // https://github.com/zloirock/core-js/issues/640
+      }, { unsafe: true });
+
+      // makes sure that native promise-based APIs `Promise#catch` properly works with patched `Promise#then`
+      redefine(NativePromisePrototype, 'catch', PromiseConstructorPrototype['catch'], { unsafe: true });
+    }
 
     // make `.constructor === Promise` work for native promise-based APIs
     try {
@@ -304,7 +311,7 @@ if (FORCED) {
 
     // make `instanceof Promise` work for native promise-based APIs
     if (setPrototypeOf) {
-      setPrototypeOf(NativePromisePrototype, PromiseConstructor.prototype);
+      setPrototypeOf(NativePromisePrototype, PromiseConstructorPrototype);
     }
   }
 }