LibJS: Implement Promise.race on the Promise constructor

2 files changed, 158 insertions, 3 deletions

diff --git a/Userland/Libraries/LibJS/Runtime/PromiseConstructor.cpp b/Userland/Libraries/LibJS/Runtime/PromiseConstructor.cpp
index 76583ba609..0905f034e8 100644
--- a/Userland/Libraries/LibJS/Runtime/PromiseConstructor.cpp
+++ b/Userland/Libraries/LibJS/Runtime/PromiseConstructor.cpp
@@ -202,6 +202,21 @@ static Value perform_promise_any(GlobalObject& global_object, Object& iterator_r
         });
 }
 
+// 27.2.4.5.1 PerformPromiseRace ( iteratorRecord, constructor, resultCapability, promiseResolve ), https://tc39.es/ecma262/#sec-performpromiserace
+static Value perform_promise_race(GlobalObject& global_object, Object& iterator_record, Value constructor, PromiseCapability result_capability, Value promise_resolve)
+{
+    auto& vm = global_object.vm();
+
+    return perform_promise_common(
+        global_object, iterator_record, constructor, result_capability, promise_resolve,
+        [&](PromiseValueList&) -> Value {
+            return result_capability.promise;
+        },
+        [&](PromiseValueList&, RemainingElements&, Value next_promise, size_t) {
+            (void)next_promise.invoke(global_object, vm.names.then, result_capability.resolve, result_capability.reject);
+        });
+}
+
 PromiseConstructor::PromiseConstructor(GlobalObject& global_object)
     : NativeFunction(vm().names.Promise.as_string(), *global_object.function_prototype())
 {
@@ -219,8 +234,7 @@ void PromiseConstructor::initialize(GlobalObject& global_object)
     define_native_function(vm.names.all, all, 1, attr);
     define_native_function(vm.names.allSettled, all_settled, 1, attr);
     define_native_function(vm.names.any, any, 1, attr);
-    // TODO: Implement these functions below and uncomment this.
-    // define_native_function(vm.names.race, race, 1, attr);
+    define_native_function(vm.names.race, race, 1, attr);
     define_native_function(vm.names.reject, reject, 1, attr);
     define_native_function(vm.names.resolve, resolve, 1, attr);
 
@@ -360,7 +374,32 @@ JS_DEFINE_NATIVE_FUNCTION(PromiseConstructor::any)
 // 27.2.4.5 Promise.race ( iterable ), https://tc39.es/ecma262/#sec-promise.race
 JS_DEFINE_NATIVE_FUNCTION(PromiseConstructor::race)
 {
-    TODO();
+    auto* constructor = vm.this_value(global_object).to_object(global_object);
+    if (!constructor)
+        return {};
+
+    auto promise_capability = new_promise_capability(global_object, constructor);
+    if (vm.exception())
+        return {};
+
+    auto promise_resolve = get_promise_resolve(global_object, constructor);
+    if (auto abrupt = if_abrupt_reject_promise(global_object, promise_resolve, promise_capability); abrupt.has_value())
+        return abrupt.value();
+
+    auto iterator_record = get_iterator(global_object, vm.argument(0));
+    if (auto abrupt = if_abrupt_reject_promise(global_object, iterator_record, promise_capability); abrupt.has_value())
+        return abrupt.value();
+
+    auto result = perform_promise_race(global_object, *iterator_record, constructor, promise_capability, promise_resolve);
+    if (vm.exception()) {
+        if (!iterator_record_is_complete(global_object, *iterator_record))
+            iterator_close(*iterator_record);
+
+        auto abrupt = if_abrupt_reject_promise(global_object, result, promise_capability);
+        return abrupt.value();
+    }
+
+    return result;
 }
 
 // 27.2.4.6 Promise.reject ( r ), https://tc39.es/ecma262/#sec-promise.reject
diff --git a/Userland/Libraries/LibJS/Tests/builtins/Promise/Promise.race.js b/Userland/Libraries/LibJS/Tests/builtins/Promise/Promise.race.js
new file mode 100644
index 0000000000..ce70452c82
--- /dev/null
+++ b/Userland/Libraries/LibJS/Tests/builtins/Promise/Promise.race.js
@@ -0,0 +1,116 @@
+test("length is 1", () => {
+    expect(Promise.race).toHaveLength(1);
+});
+
+describe("normal behavior", () => {
+    test("returns a Promise", () => {
+        const promise = Promise.race();
+        expect(promise).toBeInstanceOf(Promise);
+    });
+
+    test("resolve", () => {
+        const promise1 = Promise.resolve(3);
+        const promise2 = 42;
+        const promise3 = new Promise((resolve, reject) => {
+            resolve("foo");
+        });
+
+        let resolvedValue = null;
+        let wasRejected = false;
+
+        Promise.race([promise1, promise2, promise3]).then(
+            value => {
+                resolvedValue = value;
+            },
+            () => {
+                wasRejected = true;
+            }
+        );
+
+        runQueuedPromiseJobs();
+        expect(resolvedValue).toBe(3);
+        expect(wasRejected).toBeFalse();
+    });
+
+    test("reject", () => {
+        const promise1 = new Promise((resolve, reject) => {
+            reject("foo");
+        });
+        const promise2 = 42;
+        const promise3 = Promise.resolve(3);
+
+        let rejectionReason = null;
+        let wasResolved = false;
+
+        Promise.race([promise1, promise2, promise3]).then(
+            () => {
+                wasResolved = true;
+            },
+            reason => {
+                rejectionReason = reason;
+            }
+        );
+
+        runQueuedPromiseJobs();
+        expect(rejectionReason).toBe("foo");
+        expect(wasResolved).toBeFalse();
+    });
+});
+
+describe("exceptional behavior", () => {
+    test("cannot invoke capabilities executor twice", () => {
+        function fn() {}
+
+        expect(() => {
+            function promise(executor) {
+                executor(fn, fn);
+                executor(fn, fn);
+            }
+
+            Promise.race.call(promise, []);
+        }).toThrow(TypeError);
+
+        expect(() => {
+            function promise(executor) {
+                executor(fn, undefined);
+                executor(fn, fn);
+            }
+
+            Promise.race.call(promise, []);
+        }).toThrow(TypeError);
+
+        expect(() => {
+            function promise(executor) {
+                executor(undefined, fn);
+                executor(fn, fn);
+            }
+
+            Promise.race.call(promise, []);
+        }).toThrow(TypeError);
+    });
+
+    test("promise without resolve method", () => {
+        expect(() => {
+            function promise(executor) {}
+            Promise.race.call(promise, []);
+        }).toThrow(TypeError);
+    });
+
+    test("no parameters", () => {
+        let rejectionReason = null;
+        Promise.race().catch(reason => {
+            rejectionReason = reason;
+        });
+        runQueuedPromiseJobs();
+        expect(rejectionReason).toBeInstanceOf(TypeError);
+    });
+
+    test("non-iterable", () => {
+        let rejectionReason = null;
+        Promise.race(1).catch(reason => {
+            rejectionReason = reason;
+        });
+        runQueuedPromiseJobs();
+        expect(rejectionReason).toBeInstanceOf(TypeError);
+    });
+});