Hello,
Looks like you want to show the buttons over the task bar in the timeline area (not in the grid).
It can be implemented with the rightside and leftside text:
Here is an example where it is implemneted: http://snippet.dhtmlx.com/5/1c5c4eb2d
You won’t see buttons above projects as they ignore start_date, end_date and duration parameters, but they depend on their children, so your changes will be reset after the next rendering.
one more question, now I’m using VueJS and I put all condition and validation functions into Vue methods
How can I access Vue methods from button onclick in this case?