CodeSandbox is one of favorite code playgrounds because the editor is based on VSCode and you cannot just only run client code, you can also run server code for example an Azure Function.

Update: Issue with CodeSandbox and Function Host

There is an issue with the CodeSandbox ngnix proxy and the Azure Function host. While GET request work like expected every POST request  with a body returns an error 400. Till now the support couldn't resolve this issue. so I switched to Gitpod. However you can for post request in the terminal like:  "curl -i -H "Accept: application/json" -H "Content-Type: application/json" -X POST --data '{"name":"chris"}' http://localhost:7071/api/hello"