I am using a custom theme for my app in ionic. But it has some css and javascript dependencies except bootstrap. Could you help me how can I import these libraries to my app? Regards
It sounds like you are probably missing some Angular usage theory if you are trying to import Bootstrap into your project.
It uses a specific set of classes and they aren't out-of-the-box compatible with Angular / Ionic.
Ionic will give you a cross-device baseline set of styles so you should really work with Ionic to build upon their styles rather trying to fight it with another system.
However, to answer your questions:
You can edit app.scss and reference files in your imported packages like this:
@import '~@swimlane/ngx-datatable/release/assets/icons';
Notice the ~ at the start and then the package name, then the path to the file. You don't need to put the .css or .scss on the end but you can if you want to.
I'm not sure the best way to do this, but you can include scripts in the <head> tag by editing the index.html.
It's not something that's really done though and sounds like you are misunderstanding the way Angular / Ionic works.
It's based around building web components and you let Angular manage the actual live html. Your code that you write is TypeScript and its to interact with various API's that set the data model and then you let Angular generate the actual script.