react-id-generator | Simple and universal HTML-id generator for React | Frontend Framework library

There are a few things off with your code.

First of all the addroom in your state is a string array in your constructor, but in the handleClick method you set it like this.setState({ addroom: htmlId }) which will set it to a string and on a string type the map function is not defined, hence the error. You should add an item to the array like this.setState({ addroom: [...this.state.addroom, htmlId] })

Secondly, in your handleClick you shouldn't return jsx, if you wan to render data for your addroom array, you should do it in the render method, and in the handleClick you should just modify the addroom state variable. You can achieve this like: