Hello Debjoy,
The $taskAction is a custom property that is added to the gantt object. So, if you use Typescript, it is expected that you don’t have the types for that property. You need to manually add the types.
It is also possible that the gantt object is not available globally, so, it is expected that you get an error.
Here is an example in the snippet: https://snippet.dhtmlx.com/xosq8avn