Welcome to the Azure platform Shrikant,
If you're looking to create a NodeJS app to deploy to Azure, you can check out how to build a NodeJS app with Visual Studio Code tutorial followed by this step-by-step on getting your NodeJS app deployed.
However, if your heart is truly set on App Service Editor feature, which is completely cool, you can set your runtime stack of your web app to Node 12 LTS and set your hosting environment to Windows. Prior versions will switch your environment to back to Linux which App Service Editor (Preview) is currently not supported. Since that feature is still in preview, functionality and availability is subject to change. Therefore, I would advise providing your feedback to the product team.
Hope this helps.