(function () {
var ActivitiesListContext = {};
ActivitiesListContext.Templates = {};
ActivitiesListContext.Templates.Fields = {
    "ActivityDescription": {
            "NewForm": RenderField // this function is present in the code, but not shown here
    }
};

SPClientTemplates.TemplateManager.RegisterTemplateOverrides(ActivitiesListContext);
})();