how to change the end_date is 14 not day 15
Hello,
Gantt stores end dates in a ‘not inclusive’ format. Meaning that the end date of the task in your example will be stored as 2022-04-15 00:00 – midnight after April 14th. By default, these dates are displayed as is, so the user may get the impression that the task takes one extra day.
You can redefine the task_end_date template to change the format of the end dates of tasks in the Gantt (i.e. to include the end date in the duration of the tasks):
https://docs.dhtmlx.com/gantt/api__gantt_task_end_date_template.html
For more details on formatting end dates, see the Task end date display & Inclusive end dates article:
https://docs.dhtmlx.com/gantt/desktop__loading.html#taskenddatedisplayampinclusiveenddates
Please check the example of how it might be implemented:
https://snippet.dhtmlx.com/5i3349k4
If you meant something different, please clarify your question.