I have come up with various solutions like using inboxSDK or using gmail.js plugin. But are these the standard way of creating gmail extensions? Is there any another way? Can we use these plugins for production usage?
This may still depend on what you need to do with Gmail. You can use Gmail API in developing a chrome extension. You have to use chrome.identity to authorize your extension to make a request to Google APIs. You can also use gmail.js, but as stated in this related SO post this project isn't maintained by Google. You can also use Apps Script and make a web app then let your chrome extension send data through postMessage. Hope this helps.