LibJS: Implement Iterator.prototype.toArray

Userland/Libraries/LibJS/Runtime/CommonPropertyNames.h

@@ -512,6 +512,7 @@ namespace JS {
     P(timeZone)                              \
     P(timeZoneName)                          \
     P(timeZones)                             \
+    P(toArray)                               \
     P(toDateString)                          \
     P(toExponential)                         \
     P(toFixed)                               \

Userland/Libraries/LibJS/Runtime/IteratorPrototype.cpp

@@ -6,6 +6,7 @@
 
 #include <AK/Function.h>
 #include <LibJS/Runtime/AbstractOperations.h>
+#include <LibJS/Runtime/Array.h>
 #include <LibJS/Runtime/FunctionObject.h>
 #include <LibJS/Runtime/GlobalObject.h>
 #include <LibJS/Runtime/IteratorHelper.h>
@@ -36,6 +37,7 @@ ThrowCompletionOr<void> IteratorPrototype::initialize(Realm& realm)
     define_native_function(realm, vm.names.drop, drop, 1, attr);
     define_native_function(realm, vm.names.flatMap, flat_map, 1, attr);
     define_native_function(realm, vm.names.reduce, reduce, 1, attr);
+    define_native_function(realm, vm.names.toArray, to_array, 0, attr);
 
     return {};
 }
@@ -516,4 +518,36 @@ JS_DEFINE_NATIVE_FUNCTION(IteratorPrototype::reduce)
     }
 }
 
+// 3.1.3.8 Iterator.prototype.toArray ( ), https://tc39.es/proposal-iterator-helpers/#sec-iteratorprototype.toarray
+JS_DEFINE_NATIVE_FUNCTION(IteratorPrototype::to_array)
+{
+    auto& realm = *vm.current_realm();
+
+    // 1. Let O be the this value.
+    // 2. If O is not an Object, throw a TypeError exception.
+    auto object = TRY(this_object(vm));
+
+    // 3. Let iterated be ? GetIteratorDirect(O).
+    auto iterated = TRY(get_iterator_direct(vm, object));
+
+    // 4. Let items be a new empty List.
+    Vector<Value> items;
+
+    // 5. Repeat,
+    while (true) {
+        // a. Let next be ? IteratorStep(iterated).
+        auto next = TRY(iterator_step(vm, iterated));
+
+        // b. If next is false, return CreateArrayFromList(items).
+        if (!next)
+            return Array::create_from(realm, items);
+
+        // c. Let value be ? IteratorValue(next).
+        auto value = TRY(iterator_value(vm, *next));
+
+        // d. Append value to items.
+        TRY_OR_THROW_OOM(vm, items.try_append(value));
+    }
+}
+
 }

Userland/Libraries/LibJS/Runtime/IteratorPrototype.h

@@ -28,6 +28,7 @@ private:
     JS_DECLARE_NATIVE_FUNCTION(drop);
     JS_DECLARE_NATIVE_FUNCTION(flat_map);
     JS_DECLARE_NATIVE_FUNCTION(reduce);
+    JS_DECLARE_NATIVE_FUNCTION(to_array);
 };
 
 }

Userland/Libraries/LibJS/Tests/builtins/Iterator/Iterator.prototype.toArray.js

@@ -0,0 +1,58 @@
+describe("errors", () => {
+    test("iterator's next method throws", () => {
+        function TestError() {}
+
+        class TestIterator extends Iterator {
+            next() {
+                throw new TestError();
+            }
+        }
+
+        expect(() => {
+            new TestIterator().toArray();
+        }).toThrow(TestError);
+    });
+
+    test("value returned by iterator's next method throws", () => {
+        function TestError() {}
+
+        class TestIterator extends Iterator {
+            next() {
+                return {
+                    done: false,
+                    get value() {
+                        throw new TestError();
+                    },
+                };
+            }
+        }
+
+        expect(() => {
+            new TestIterator().toArray();
+        }).toThrow(TestError);
+    });
+});
+
+describe("normal behavior", () => {
+    test("length is 0", () => {
+        expect(Iterator.prototype.toArray).toHaveLength(0);
+    });
+
+    test("empty list", () => {
+        function* generator() {}
+
+        const result = generator().toArray();
+        expect(result).toEqual([]);
+    });
+
+    test("non-empty list", () => {
+        function* generator() {
+            yield 1;
+            yield 2;
+            yield 3;
+        }
+
+        const result = generator().toArray();
+        expect(result).toEqual([1, 2, 3]);
+    });
+});