For example, if your ICalendarProps interface has the following properties: error TS2339: Property '_input' does not exist on type 'FileUpload'. Have a question about this project? In addition to @iffy and @RyanCavanaugh global namespace solution, you can declare your custom element type like this: In order to get better type/property checking and code completion on your custom tags, @TheAfterman Can you help me modify your solution to work with components such as will be rendered into , and all the properties which are not listed above will be transferred to the