In comparison to Angular (2 and higher), AngularJS has several important limitations that affect the way applications can be built.
A single injector with string DI tokens and no built-in lazy loading.
Config/run phases and synchronous bootstrapping (the overview of configuration recipes).
Scope hierarchy for data binding and its consequences for application architecture - the concept of digests, performance impact, AngularJS-specific services ($timeout, $q, ...) instead of native counterparts, etc.
jQuery-influenced approaches for manual DOM manipulation.
Considerably different set and API of built-in services, directives and filters (pipes).
No support for nested applications (possible with a hack).
No view encapsulation and component styles.
No built-in component router.
No built-in translation/i18n.
No built-in support for workers and server side rendering.
No official CLI.
The development of AngularJS has been focused on providing upgrade strategies and common features since 1.5. In a lot of aspects Angular/TypeScript experience can serve as a source for best practices for modern AngularJS development.
AngularJS is generally more flexible in the ways how its injector and compiler work and allows for a plethora of neat hacks that have been rendered impractical or impossible in Angular.
There's a lot of smaller differences that AngularJS introduces which may be discarded if the goal is to intentionally limit development practices to the ones that allow to build TypeScript/ES6/ES.next AngularJS application that follows Angular guidelines and could be easily upgraded to Angular in future.
ng-metadata does its best to unify AngularJS coding practices with Angular but still requires a good understanding of the differences between two frameworks.
However, smaller differences make a big difference if a developer works on existing AngularJS project that heavily relies on them and uses legacy coding standards.
