WebContent: Add `$_` variable to browser console

This holds the return value of the expression that was last entered into
the browser console. If that last expression returned an error of some
kind, `$_` will be `undefined`. This matches the behaviour in Firefox.

3 files changed, 15 insertions, 1 deletions

diff --git a/Userland/Services/WebContent/ConsoleGlobalObject.cpp b/Userland/Services/WebContent/ConsoleGlobalObject.cpp
index 9b76e42d44..45e9dd8e5d 100644
--- a/Userland/Services/WebContent/ConsoleGlobalObject.cpp
+++ b/Userland/Services/WebContent/ConsoleGlobalObject.cpp
@@ -22,6 +22,7 @@ void ConsoleGlobalObject::initialize(JS::Realm& realm)
     Base::initialize(realm);
 
     define_native_accessor(realm, "$0", $0_getter, nullptr, 0);
+    define_native_accessor(realm, "$_", $__getter, nullptr, 0);
 }
 
 void ConsoleGlobalObject::visit_edges(Visitor& visitor)
@@ -110,4 +111,10 @@ JS_DEFINE_NATIVE_FUNCTION(ConsoleGlobalObject::$0_getter)
     return inspected_node;
 }
 
+JS_DEFINE_NATIVE_FUNCTION(ConsoleGlobalObject::$__getter)
+{
+    auto* console_global_object = TRY(get_console(vm));
+    return console_global_object->m_most_recent_result;
+}
+
 }
diff --git a/Userland/Services/WebContent/ConsoleGlobalObject.h b/Userland/Services/WebContent/ConsoleGlobalObject.h
index 1cb4758127..e4abdfc287 100644
--- a/Userland/Services/WebContent/ConsoleGlobalObject.h
+++ b/Userland/Services/WebContent/ConsoleGlobalObject.h
@@ -33,13 +33,18 @@ public:
     virtual JS::ThrowCompletionOr<bool> internal_delete(JS::PropertyKey const& name) override;
     virtual JS::ThrowCompletionOr<JS::MarkedVector<JS::Value>> internal_own_property_keys() const override;
 
+    void set_most_recent_result(JS::Value result) { m_most_recent_result = move(result); }
+
 private:
     virtual void visit_edges(Visitor&) override;
 
     // $0, the DOM node currently selected in the inspector
     JS_DECLARE_NATIVE_FUNCTION($0_getter);
+    // $_, the value of the most recent expression entered into the console
+    JS_DECLARE_NATIVE_FUNCTION($__getter);
 
     Web::HTML::Window* m_window_object;
+    JS::Value m_most_recent_result { JS::js_undefined() };
 };
 
 }
diff --git a/Userland/Services/WebContent/WebContentConsoleClient.cpp b/Userland/Services/WebContent/WebContentConsoleClient.cpp
index e7767f3060..f72da8df8d 100644
--- a/Userland/Services/WebContent/WebContentConsoleClient.cpp
+++ b/Userland/Services/WebContent/WebContentConsoleClient.cpp
@@ -77,8 +77,10 @@ void WebContentConsoleClient::handle_input(String const& js_source)
 
     auto result = script->run();
 
-    if (result.value().has_value())
+    if (result.value().has_value()) {
+        m_console_global_object->set_most_recent_result(result.value().value());
         print_html(JS::MarkupGenerator::html_from_value(*result.value()));
+    }
 }
 
 void WebContentConsoleClient::report_exception(JS::Error const& exception, bool in_promise)