Its easy for a beginner to get lost and be overwhelmed by the plethora of libraries, frameworks, apps and all kinds of popular components in the JS world.
One wonders sometimes about what to learn, where to begin and most importantly, where to stop and consolidate our learning and build something useful using that knowledge.
$.post()and other DOM manipulation techniques, compliments of jquery. The enterprises still use it a lot and even the latest version of bootstrap still uses jquery.
Angular: Angular (formerly angular.js) is a single page app framework that became popular right since day one, partly thanks to Google who is the founder and patron of the software. Its a comprehensive framework that lets you define an MVC workflow with relative ease.
However, the biggest criticism against angular is that its highly opinionated and complex under the hoods. The relative ease of defining ng-directives, services, routes, etc. comes with a cost - which is lack of backward incompatibility coupled with this facade of a highly complex beast under the hoods.
The lack of backward compatibility is especially problematic as it left many users stranded when the while ecosystem migrated to the new 2.x version powered by TypeScript. Nevertheless, its knowledge is important if you wish to get projects in the webdev world today.
React: React is the V (View) portion of the MVC and more of a library or toolkit than framework. As such, it gained rapid fame and popularity in webdev world in a short time, this time thanks to Facebook who is the prime contributor and proponent of this tech.
Vue.js - I haven't gotten around tinkering vue much yet but suffice it to say that its another framework mostly comprising the view part again, and much simpler to use than angular.
Bootstrap - Bootstrap is like the bread and butter of the webdev world. Its popularity can be attributed to the fact that even a non-designer without any expertise in CSS/JS can easily integrate it into their apps, coupled with its helpful classes for layouts and presentation which are quite easy to learn.