Prevent closing webview if the user didn't save the changes

[bk201-]

Hi, I'm a developer of Azure CosmosDB extension.

Using extension the user can edit cosmosdb documents in webview tab. However, webview doesn't have onBeforeUnload event or similar functionality to prevent closing webview when the user edited the document, if the user close webview tab it always closes without any prompt like confirmation dialog for unsaved document.

This would be useful if vscode provides functionality to prevent closing webview.

[mjbvz]

Try using a custom editor: https://code.visualstudio.com/api/extension-guides/custom-editors

Custom editors have dirty state tracking and saving, just like with normal text editors. They also can be used with virtual documents or virtual file systems