refactoring and optimization

[Wojciech Pela]

refactoring and optimization

[Daniel Fidor]

• Remove repetitive code (eg. PrivateRoute's validate function)
• Add interfaces and/or types instead of any
• Prettify code
• Remove "solvable" eslint-disable's
• Add error handling
• Remove unused vars
• Remove unused, commented code
• Fix router - move "layout specific" divs to views
• Extract repetitive utility classes to single classes - similar to your .btn classes
• Move similar components to folders (eg. AddBook and UpdateBook in single directory)
• Maybe add prop to sidebar that will decide what's inside, and remove SidebarAdmin? I think it would remove the need to change classes in both files when you decide to change sidebar styles.
• Use consistent function type - I'd prefer arrow function - and add FC type to them
• Remove <br> where it isn't explicitly needed and prefer to style such things with css
• Replace placeholders such as "siema" and replace them with suitable messages
• Add and display loading and error state to requests
• Make sure the file name is the same as component name
• Be awesome! :3