LibJS: Add the TypedArray.from() method

3 files changed, 114 insertions, 0 deletions

diff --git a/Userland/Libraries/LibJS/Runtime/TypedArrayConstructor.cpp b/Userland/Libraries/LibJS/Runtime/TypedArrayConstructor.cpp
index 3646bbb4dd..14a5d8c764 100644
--- a/Userland/Libraries/LibJS/Runtime/TypedArrayConstructor.cpp
+++ b/Userland/Libraries/LibJS/Runtime/TypedArrayConstructor.cpp
@@ -5,6 +5,7 @@
  */
 
 #include <LibJS/Runtime/GlobalObject.h>
+#include <LibJS/Runtime/IteratorOperations.h>
 #include <LibJS/Runtime/TypedArray.h>
 #include <LibJS/Runtime/TypedArrayConstructor.h>
 
@@ -31,6 +32,7 @@ void TypedArrayConstructor::initialize(GlobalObject& global_object)
     define_property(vm.names.length, Value(0), Attribute::Configurable);
 
     u8 attr = Attribute::Writable | Attribute::Configurable;
+    define_native_function(vm.names.from, from, 1, attr);
     define_native_function(vm.names.of, of, 0, attr);
 
     define_native_accessor(*vm.well_known_symbol_species(), symbol_species_getter, {}, Attribute::Configurable);
@@ -80,6 +82,89 @@ static TypedArrayBase* typed_array_create(GlobalObject& global_object, FunctionO
     return &typed_array;
 }
 
+// 23.2.2.1 %TypedArray%.from ( source [ , mapfn [ , thisArg ] ] ), https://tc39.es/ecma262/#sec-%typedarray%.from
+JS_DEFINE_NATIVE_FUNCTION(TypedArrayConstructor::from)
+{
+    auto constructor = vm.this_value(global_object);
+    if (!constructor.is_constructor()) {
+        vm.throw_exception<TypeError>(global_object, ErrorType::NotAConstructor, constructor.to_string_without_side_effects());
+        return {};
+    }
+
+    FunctionObject* map_fn = nullptr;
+    if (!vm.argument(1).is_undefined()) {
+        auto callback = vm.argument(1);
+        if (!callback.is_function()) {
+            vm.throw_exception<TypeError>(global_object, ErrorType::NotAFunction, callback.to_string_without_side_effects());
+            return {};
+        }
+        map_fn = &callback.as_function();
+    }
+
+    auto source = vm.argument(0);
+    auto this_arg = vm.argument(2);
+
+    auto using_iterator = source.get_method(global_object, *vm.well_known_symbol_iterator());
+    if (vm.exception())
+        return {};
+    if (using_iterator) {
+        auto values = iterable_to_list(global_object, source, using_iterator);
+        if (vm.exception())
+            return {};
+
+        MarkedValueList arguments(vm.heap());
+        arguments.empend(values.size());
+        auto target_object = typed_array_create(global_object, constructor.as_function(), move(arguments));
+        if (vm.exception())
+            return {};
+
+        for (size_t k = 0; k < values.size(); ++k) {
+            auto k_value = values[k];
+            Value mapped_value;
+            if (map_fn) {
+                mapped_value = vm.call(*map_fn, this_arg, k_value, Value(k));
+                if (vm.exception())
+                    return {};
+            } else {
+                mapped_value = k_value;
+            }
+            target_object->set(k, mapped_value, true);
+            if (vm.exception())
+                return {};
+        }
+
+        return target_object;
+    }
+
+    auto array_like = source.to_object(global_object);
+    auto length = length_of_array_like(global_object, *array_like);
+    if (vm.exception())
+        return {};
+
+    MarkedValueList arguments(vm.heap());
+    arguments.empend(length);
+    auto target_object = typed_array_create(global_object, constructor.as_function(), move(arguments));
+    if (vm.exception())
+        return {};
+
+    for (size_t k = 0; k < length; ++k) {
+        auto k_value = array_like->get(k);
+        Value mapped_value;
+        if (map_fn) {
+            mapped_value = vm.call(*map_fn, this_arg, k_value, Value(k));
+            if (vm.exception())
+                return {};
+        } else {
+            mapped_value = k_value;
+        }
+        target_object->set(k, mapped_value, true);
+        if (vm.exception())
+            return {};
+    }
+
+    return target_object;
+}
+
 // 23.2.2.2 %TypedArray%.of ( ...items ), https://tc39.es/ecma262/#sec-%typedarray%.of
 JS_DEFINE_NATIVE_FUNCTION(TypedArrayConstructor::of)
 {
diff --git a/Userland/Libraries/LibJS/Runtime/TypedArrayConstructor.h b/Userland/Libraries/LibJS/Runtime/TypedArrayConstructor.h
index 5b2c3ff9ae..c113b255e1 100644
--- a/Userland/Libraries/LibJS/Runtime/TypedArrayConstructor.h
+++ b/Userland/Libraries/LibJS/Runtime/TypedArrayConstructor.h
@@ -25,6 +25,7 @@ public:
 private:
     virtual bool has_constructor() const override { return true; }
 
+    JS_DECLARE_NATIVE_FUNCTION(from);
     JS_DECLARE_NATIVE_FUNCTION(of);
     JS_DECLARE_NATIVE_GETTER(symbol_species_getter);
 };
diff --git a/Userland/Libraries/LibJS/Tests/builtins/TypedArray/TypedArray.from.js b/Userland/Libraries/LibJS/Tests/builtins/TypedArray/TypedArray.from.js
new file mode 100644
index 0000000000..074d6e605c
--- /dev/null
+++ b/Userland/Libraries/LibJS/Tests/builtins/TypedArray/TypedArray.from.js
@@ -0,0 +1,28 @@
+const TYPED_ARRAYS = [
+    Uint8Array,
+    Uint16Array,
+    Uint32Array,
+    Int8Array,
+    Int16Array,
+    Int32Array,
+    Float32Array,
+    Float64Array,
+];
+
+const BIGINT_TYPED_ARRAYS = [BigUint64Array, BigInt64Array];
+
+test("basic functionality", () => {
+    TYPED_ARRAYS.forEach(T => {
+        const newTypedArray = T.from([1, 2, 3]);
+        expect(newTypedArray[0]).toBe(1);
+        expect(newTypedArray[1]).toBe(2);
+        expect(newTypedArray[2]).toBe(3);
+    });
+
+    BIGINT_TYPED_ARRAYS.forEach(T => {
+        const newTypedArray = T.from([1n, 2n, 3n]);
+        expect(newTypedArray[0]).toBe(1n);
+        expect(newTypedArray[1]).toBe(2n);
+        expect(newTypedArray[2]).toBe(3n);
+    });
+});