You could consider using https://developer.mozilla.org/en-US/docs/Glossary/IIFE#avoid_polluting_the_global_namespace

Your shared JS would be an IIFE that you call with a config object like

    <script>
        initializeMapLogic({
          bgLayerName : '@Model.DefaultBackgroundLayer',
          infoLayerName : '@Model.DefaultInformationLayer',
          onlyEnablePolygon : true,
          allowMultiplePolygons : true
        });
    </script>