How Programming Languages Differ, and What Frameworks and Libraries Are

This article covers how programming languages differ, and what frameworks and libraries are.

You will be able to tell whether a name such as React or Next.js is a language or something written in a language.

It covers Python and JavaScript, plus four names: React, Next.js, Django, and Flutter.

What a programming language is — different syntax, the same content

A programming language (the vocabulary and writing rules for source code) is paired with a runtime.

What differs is the syntax (the rules for which symbols and word order you write an instruction in).

Python marks a block with a colon at the end of the line and indentation, and JavaScript marks it with ; and { }.

Of the next four lines, the first three are written the JavaScript way and the last one the Python way.

let a = 3;
let b = 4;
console.log(a + b);
console.log(len([a, b]))

After the third line prints 7, it stops at the last line.

Even when you want the same thing, the runtime cannot read it if the way you write it is different.

Languages differ in how you write, not in what you do

A programming language is the set of rules for the symbols and word order you use when writing code.

Giving a value a name, branching on a condition, and repeating exist in every language, and what differs is only how you write them and the runtime that reads them.

Libraries and frameworks — the call runs in opposite directions

A library and a framework are both collections of programs other people wrote, and you use them to write less yourself.

Naming a feature of another program and having it run is what calling it means.

The difference between the two is the direction of that call.

In the lower frame the inside and the outside swap, and the framework calls your own code.

Whichever is on the outside decides the overall flow.

Calling a library takes one line instead of the dozens you would write yourself.

The only difference is who wrote that processing.

A library that has to be installed before you call it will stop with an error if you call it without installing it.

Guides also call these "packages" and "modules," and how that works is covered in the article "What Package Management Is."

A web app framework holds the flow from receiving a request to returning a response.

The three on the outside are done by the framework, so you do not write them.

The reason to use a framework is to avoid writing the outside yourself.

Your own code runs only in the third step, and the framework handles what comes before and after.

Which URL runs which piece of code is likewise just written in a set place.

Calling, or being called

A library and a framework are both programs other people wrote, and the difference is which one is on the outside.

A library is called from inside your own code, and a framework calls your own code from outside and decides the overall flow.

What React, Next.js, Django, and Flutter are — sorting names into three kinds

You read the names that come up in a course by sorting each one into language, library, or framework.

Next.js is not a language; it is a framework written in JavaScript.

React is a library that builds the parts of a screen, and Next.js is a framework that uses that React and goes as far as server-side processing.

Flutter is a framework for building phone apps, and you write it in a language called Dart.

Being able to build an app that runs on several operating systems from one set of code is called cross-platform.

None of these names is a language; each is something you use together with your own code.

The same name, Next.js, appears on both the device side and the server side.

That is because what it covers changes with whether it only builds the screen or also holds the server-side processing.

Even from a phone app built with Flutter, what it connects to is the same public server.

Is the name a language, or something written in a language

Next.js, React, Django, and Flutter are not languages; each is written in some language.

Looking up which language you write it in tells you whether it is a language itself, and looking up the direction of the call tells you whether it is a library or a framework.

Which language to learn first — decide by whether what you want to build needs a screen in the browser

The language a browser can read is JavaScript, so the screen side (the frontend) is JavaScript.

The processing side (the backend) runs on the server, so you can write it in either.

If you need a screen in the browser, that part is settled as JavaScript.

If you do not need a screen, start with Python, which has many external libraries for data analysis and automation.

The frameworks and libraries in the bottom row come after you choose a language; they are not what you choose first.

Whichever you start with, the mechanisms you learn are the same.

The two paths meet at the same place in the end.

What you relearn is the way of writing and the names of the libraries used in that language.

Choose the one closer to what you want to build, and move ahead with it.

Once what you want to build is decided, the language is decided

You can settle the language by what you want to build, not by preference.

If you need a screen that runs in the browser, that part is JavaScript, and if you do not, you can start with Python, and for a second language what you relearn is only the way of writing and the names of the libraries.