LibJS: Add spec comments to DataViewConstructor

Userland/Libraries/LibJS/Runtime/DataViewConstructor.cpp

@@ -34,6 +34,8 @@ void DataViewConstructor::initialize(Realm& realm)
 ThrowCompletionOr<Value> DataViewConstructor::call()
 {
     auto& vm = this->vm();
+
+    // 1. If NewTarget is undefined, throw a TypeError exception.
     return vm.throw_completion<TypeError>(ErrorType::ConstructorWithoutNew, vm.names.DataView);
 }
 
@@ -43,35 +45,58 @@ ThrowCompletionOr<NonnullGCPtr<Object>> DataViewConstructor::construct(FunctionO
     auto& vm = this->vm();
 
     auto buffer = vm.argument(0);
+    auto byte_offset = vm.argument(1);
+    auto byte_length = vm.argument(2);
+
+    // 2. Perform ? RequireInternalSlot(buffer, [[ArrayBufferData]]).
     if (!buffer.is_object() || !is<ArrayBuffer>(buffer.as_object()))
         return vm.throw_completion<TypeError>(ErrorType::IsNotAn, buffer.to_string_without_side_effects(), vm.names.ArrayBuffer);
 
     auto& array_buffer = static_cast<ArrayBuffer&>(buffer.as_object());
 
-    auto offset = TRY(vm.argument(1).to_index(vm));
+    // 3. Let offset be ? ToIndex(byteOffset).
+    auto offset = TRY(byte_offset.to_index(vm));
 
+    // 4. If IsDetachedBuffer(buffer) is true, throw a TypeError exception.
     if (array_buffer.is_detached())
         return vm.throw_completion<TypeError>(ErrorType::DetachedArrayBuffer);
 
+    // 5. Let bufferByteLength be buffer.[[ArrayBufferByteLength]].
     auto buffer_byte_length = array_buffer.byte_length();
+
+    // 6. If offset > bufferByteLength, throw a RangeError exception.
     if (offset > buffer_byte_length)
         return vm.throw_completion<RangeError>(ErrorType::DataViewOutOfRangeByteOffset, offset, buffer_byte_length);
 
     size_t view_byte_length;
-    if (vm.argument(2).is_undefined()) {
+
+    // 7. If byteLength is undefined, then
+    if (byte_length.is_undefined()) {
+        // a. Let viewByteLength be bufferByteLength - offset.
         view_byte_length = buffer_byte_length - offset;
-    } else {
+    }
-        view_byte_length = TRY(vm.argument(2).to_index(vm));
+    // 8. Else,
+    else {
+        // a. Let viewByteLength be ? ToIndex(byteLength).
+        view_byte_length = TRY(byte_length.to_index(vm));
+
+        // b. If offset + viewByteLength > bufferByteLength, throw a RangeError exception.
         auto const checked_add = AK::make_checked(view_byte_length) + AK::make_checked(offset);
         if (checked_add.has_overflow() || checked_add.value() > buffer_byte_length)
             return vm.throw_completion<RangeError>(ErrorType::InvalidLength, vm.names.DataView);
     }
 
+    // 9. Let O be ? OrdinaryCreateFromConstructor(NewTarget, "%DataView.prototype%", « [[DataView]], [[ViewedArrayBuffer]], [[ByteLength]], [[ByteOffset]] »).
+    // 11. Set O.[[ViewedArrayBuffer]] to buffer.
+    // 12. Set O.[[ByteLength]] to viewByteLength.
+    // 13. Set O.[[ByteOffset]] to offset.
     auto data_view = TRY(ordinary_create_from_constructor<DataView>(vm, new_target, &Intrinsics::data_view_prototype, &array_buffer, view_byte_length, offset));
 
+    // 10. If IsDetachedBuffer(buffer) is true, throw a TypeError exception.
     if (array_buffer.is_detached())
         return vm.throw_completion<TypeError>(ErrorType::DetachedArrayBuffer);
 
+    // 14. Return O.
     return data_view;
 }