What is Angular ?
What is a Single Page Application?
More or less like you mobile application, everything you see in the same page and rendered in the browser, and whenever you need a data it's happened in the background without changing the page you are on.
How it's done?
Angular is changing the dom without the need to change the page.
Angular 2 vs Angular 4
- Angular 1 was the first AngularJS and it was a great user experience.
- Angular 2 was a rewrite and totally new and has nothing to do with Angular 1 , so if you don't know any of them then i don't advise you to learn Angular 1 and just jump to 2.
- Angular 4 is not a complete rewrite but just some tweaks to Angular 2, Angular 3 was skipped for versioning conflicts.