The front and back end interaction of add, delete and change

Light box inside the save delete button, click the need to request api to the background, rather than the front desk directly delete, please ask how to get the background response data before deciding whether to close the light box. If the background response is slow, how to do a loading on the button to prompt the user to request data

Hello Ethan,
DHTMLX Gantt is a client-side library. So, when you make any changes, they occur only inside the browser, then, if you configured Gantt, they are sent to the server. So, you need to customize Gantt to fit your needs.
If you don’t want to allow users to close the lightbox when they click on the Save and Delete buttons, you can return false in the onLightboxSave and onLightboxDelete event handlers:
https://docs.dhtmlx.com/gantt/api__gantt_onlightboxsave_event.html
https://docs.dhtmlx.com/gantt/api__gantt_onlightboxdelete_event.html

After a successful response from the server, you can update the task and link data with the Gantt API, then you can close the lightbox with the hideLightbox method:
https://docs.dhtmlx.com/gantt/api__gantt_hidelightbox.html

Here is an example of how it can be implemented:
https://snippet.dhtmlx.com/0dcfo1ye

There is no built-in way to show the loading icon. You need to manually add it by using the Gantt API and Javascript. The easiest way to do that would be to modify the DOM structure.
To load the data from the server, you can use the parse and load methods:
https://docs.dhtmlx.com/gantt/api__gantt_parse.html
https://docs.dhtmlx.com/gantt/api__gantt_load.html