I cannot understand the concept of JavaScript frameworks.

Something like VueJS lets you implement JavaScript logic directly into your HTML. It abstracts away the code and let's you just do what you need to do with the data.

Example, let's say we have an array,

let fruit = ['apple', 'banana', 'orange']

How much code would you need to write to turn that into a HTML list? and to make that HTML list update dynamically every time the value of fruit changed?

This is what it looks like in Vue:

<ul>
    <li v-for="item in fruit">
</ul>

This will read and iterate over fruit and render for each one a li element.

The power comes when you update how many items there are in fruit. Vue is smart enough to update your HTML! So if we add strawberry to the list later on, it will dynamically be added.

Take a super quick crash course on Vue here: vuejs.org/v2/guide/#Declarative-Re... and you'll quickly realize how dynamic and powerful it can make your UIs and web applications.

From a fundamental perspective, a framework allows you to rely on millions of hours of other people's expertise instead of re-inventing the wheel for yourself.

Hypothetically, you could build a raw JavaScript application which uses no frameworks, but it would be incredibly time-consuming to code things like state management, interface components, routing, etc. If you are approaching the language as a beginner, it would take you decades to learn all of language intricacies that a framework will do for you.

So for example, you want to create a simple inventory management application where users can browse and select items. React, Vue, and Angular (and others) have simplified the process of generating interface components and making them communicate across the application and with the backend.

I am assuming you are a beginner (which is awesome, you have a long and rewarding road ahead of you) - it is essential you learn the fundamentals of the JavaScript language. Those fundamentals will probably be enough to land you a first job, but if you want to build full application front-ends, you will need to explore a framework. The major ones all have pros and cons, along with their supporters and haters.

But ultimately they are all tools which help package up the power of a programming language and solve lots of the implementation projects for you. The open source community is awesome because very very smart people have solved some complicated problems, and simplified them for you and me.