diff --git a/Libraries/LibWeb/DOM/Document.cpp b/Libraries/LibWeb/DOM/Document.cpp
index 51e68f80b9..3ff49702dd 100644
--- a/Libraries/LibWeb/DOM/Document.cpp
+++ b/Libraries/LibWeb/DOM/Document.cpp
@@ -51,10 +51,10 @@
 #include <LibWeb/DOM/Window.h>
 #include <LibWeb/Dump.h>
 #include <LibWeb/Frame.h>
-#include <LibWeb/PageView.h>
 #include <LibWeb/Layout/LayoutDocument.h>
 #include <LibWeb/Layout/LayoutTreeBuilder.h>
 #include <LibWeb/Origin.h>
+#include <LibWeb/PageView.h>
 #include <LibWeb/Parser/CSSParser.h>
 #include <stdio.h>
 
@@ -429,4 +429,24 @@ NonnullRefPtr<HTMLScriptElement> Document::take_pending_parsing_blocking_script(
     return m_pending_parsing_blocking_script.release_nonnull();
 }
 
+void Document::add_script_to_execute_when_parsing_has_finished(Badge<HTMLScriptElement>, HTMLScriptElement& script)
+{
+    m_scripts_to_execute_when_parsing_has_finished.append(script);
+}
+
+NonnullRefPtrVector<HTMLScriptElement> Document::take_scripts_to_execute_when_parsing_has_finished(Badge<HTMLDocumentParser>)
+{
+    return move(m_scripts_to_execute_when_parsing_has_finished);
+}
+
+void Document::add_script_to_execute_as_soon_as_possible(Badge<HTMLScriptElement>, HTMLScriptElement& script)
+{
+    m_scripts_to_execute_as_soon_as_possible.append(script);
+}
+
+NonnullRefPtrVector<HTMLScriptElement> Document::take_scripts_to_execute_as_soon_as_possible(Badge<HTMLDocumentParser>)
+{
+    return move(m_scripts_to_execute_as_soon_as_possible);
+}
+
 }
diff --git a/Libraries/LibWeb/DOM/Document.h b/Libraries/LibWeb/DOM/Document.h
index ee72d54c1a..37db176127 100644
--- a/Libraries/LibWeb/DOM/Document.h
+++ b/Libraries/LibWeb/DOM/Document.h
@@ -133,6 +133,12 @@ public:
     HTMLScriptElement* pending_parsing_blocking_script() { return m_pending_parsing_blocking_script; }
     NonnullRefPtr<HTMLScriptElement> take_pending_parsing_blocking_script(Badge<HTMLDocumentParser>);
 
+    void add_script_to_execute_when_parsing_has_finished(Badge<HTMLScriptElement>, HTMLScriptElement&);
+    NonnullRefPtrVector<HTMLScriptElement> take_scripts_to_execute_when_parsing_has_finished(Badge<HTMLDocumentParser>);
+
+    void add_script_to_execute_as_soon_as_possible(Badge<HTMLScriptElement>, HTMLScriptElement&);
+    NonnullRefPtrVector<HTMLScriptElement> take_scripts_to_execute_as_soon_as_possible(Badge<HTMLDocumentParser>);
+
     bool in_quirks_mode() const { return m_quirks_mode; }
     void set_quirks_mode(bool mode) { m_quirks_mode = mode; }
 
@@ -161,6 +167,8 @@ private:
     OwnPtr<JS::Interpreter> m_interpreter;
 
     RefPtr<HTMLScriptElement> m_pending_parsing_blocking_script;
+    NonnullRefPtrVector<HTMLScriptElement> m_scripts_to_execute_when_parsing_has_finished;
+    NonnullRefPtrVector<HTMLScriptElement> m_scripts_to_execute_as_soon_as_possible;
 
     bool m_quirks_mode { false };
 };
diff --git a/Libraries/LibWeb/DOM/HTMLScriptElement.cpp b/Libraries/LibWeb/DOM/HTMLScriptElement.cpp
index df9e1df5f6..f0fe745486 100644
--- a/Libraries/LibWeb/DOM/HTMLScriptElement.cpp
+++ b/Libraries/LibWeb/DOM/HTMLScriptElement.cpp
@@ -206,10 +206,7 @@ void HTMLScriptElement::prepare_script(Badge<HTMLDocumentParser>)
 
     // FIXME: Check classic vs. module
     if (has_attribute("src") && has_attribute("defer") && m_parser_inserted && !has_attribute("async")) {
-        // FIXME: Add the element to the end of the list of scripts that will execute
-        //        when the document has finished parsing associated with the Document
-        //        of the parser that created the element.
-        ASSERT_NOT_REACHED();
+        document().add_script_to_execute_when_parsing_has_finished({}, *this);
     }
 
     else if (has_attribute("src") && m_parser_inserted && !has_attribute("async")) {
@@ -225,7 +222,7 @@ void HTMLScriptElement::prepare_script(Badge<HTMLDocumentParser>)
     }
 
     else if (has_attribute("src")) {
-        ASSERT_NOT_REACHED();
+        m_preparation_time_document->add_script_to_execute_as_soon_as_possible({}, *this);
     }
 
     else {
diff --git a/Libraries/LibWeb/Parser/HTMLDocumentParser.cpp b/Libraries/LibWeb/Parser/HTMLDocumentParser.cpp
index e524fe0edd..a985f846d1 100644
--- a/Libraries/LibWeb/Parser/HTMLDocumentParser.cpp
+++ b/Libraries/LibWeb/Parser/HTMLDocumentParser.cpp
@@ -80,7 +80,17 @@ void HTMLDocumentParser::run(const URL& url)
 
     // "The end"
 
+    auto scripts_to_execute_when_parsing_has_finished = m_document->take_scripts_to_execute_when_parsing_has_finished({});
+    for (auto& script : scripts_to_execute_when_parsing_has_finished) {
+        script.execute_script();
+    }
+
     m_document->dispatch_event(Event::create("DOMContentLoaded"));
+
+    auto scripts_to_execute_as_soon_as_possible = m_document->take_scripts_to_execute_as_soon_as_possible({});
+    for (auto& script : scripts_to_execute_as_soon_as_possible) {
+        script.execute_script();
+    }
 }
 
 void HTMLDocumentParser::process_using_the_rules_for(InsertionMode mode, HTMLToken& token)