SPFx loaders and SPe.js library. Customizing modern SharePoint with JavaScript.
Introduction - https://youtu.be/1UXDuEri0D4
Custom Branding, Tabs and Chart - https://youtu.be/33GZQfHiKpM
Customize List Views and Forms - https://youtu.be/yjb6xR2j9k0
Move JavaScript customizations to modern SharePoint - https://youtu.be/4ieloE06B08
Advanced modern SharePoint list form customizations - https://youtu.be/heREQOU_i5o