Support es modules in js includes (#2063)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

nbconvert/exporters/html.py

@@ -304,10 +304,10 @@ def resources_include_lab_theme(name):
             code = """<style type="text/css">\n%s</style>""" % data
             return markupsafe.Markup(code)
 
-        def resources_include_js(name):
-            """Get the resources include JS for a name."""
+        def resources_include_js(name, module=False):
+            """Get the resources include JS for a name. If module=True, import as ES module"""
             env = self.environment
-            code = """<script>\n%s</script>""" % (env.loader.get_source(env, name)[0])
+            code = f"""<script {'type="module"' if module else ""}>\n{env.loader.get_source(env, name)[0]}</script>"""
             return markupsafe.Markup(code)
 
         def resources_include_url(name):

tests/exporters/files/esmodule.html.j2

@@ -0,0 +1,4 @@
+{%- extends 'lab/index.html.j2' -%}
+{%- block html_head_js -%}
+{{ resources.include_js("esmodule.js", True) }}
+{%- endblock html_head_js -%}

tests/exporters/files/esmodule.js

@@ -0,0 +1,2 @@
+const blerg = true
+export { blerg };

tests/exporters/test_templateexporter.py

@@ -307,6 +307,15 @@ def test_local_template_file_extending_lab(self):
         output, resources = exporter.from_notebook_node(nb)
         assert "UNIQUE" in output
 
+    def test_local_template_file_esmodule_js(self):
+        template_file = os.path.join(self._get_files_path(), "esmodule.html.j2")
+        exporter = HTMLExporter(template_file=template_file, template_name="lab")
+        nb = v4.new_notebook()
+        nb.cells.append(v4.new_code_cell("some_text"))
+        output, resources = exporter.from_notebook_node(nb)
+        print(output[:1000])
+        assert '<script type="module">\nconst blerg = true' in output
+
     def test_raw_template_attr(self):
         """
         Verify that you can assign a in memory template string by overwriting