I am working on SharePoint office 365 (2016), and facing issue while adding custom validation in new item form.  

Here scenario is complex, I can't handle by using Validation setting/formula. So I have choose custom JavaScript code.  

As validation should be perform on click of Save button and PreSaveAction method successfully called but only in 'Classic Experience' but when user changed to 'New Experience' it won't call because of change of HTML structure of the form.   

Does any one have an idea how to fix this issue?
Thanks in advance!