API Reference > imodeljs-frontend > QuantityFormatting > isCustomQuantityTypeDefinition isCustomQuantityTypeDefinition Function Beta CustomQuantityTypeDefinition type guard. isCustomQuantityTypeDefinition(item: QuantityTypeDefinition): item is CustomQuantityTypeDefinition Parameter Type Description item QuantityTypeDefinition Returns - item is CustomQuantityTypeDefinition Defined in core/frontend/src/quantity-formatting/QuantityFormatter.ts Line 156 Last Updated: 29 November, 2022