Concaténer les variables et les chaînes en réaction
href={"#demo" + this.state.id}
//You can also use ES6 string interpolation/template literals with
//` (backticks) and ${expr} (interpolated expression),
href={`#demo${this.state.id}`}
source
https://stackoverflow.com/questions/39523040/concatenating-variables-and-strings-in-react
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