Javascript

JavaScript is one of the most popular programming languages in the world, and now widely used also outside of the browser. The rise of Node.js in the last few years unlocked backend development, once the domain of Java, Ruby, Python, PHP, and more traditional server-side languages.

JavaScript is one of the 3 languages all web developers must learn:

   1. HTML to define the content of web pages

   2. CSS to specify the layout of web pages

   3. JavaScript to program the behavior of web pages

Web pages are not the only place where JavaScript is used. Many desktop and server programs use JavaScript. Node.js is the best known. Some databases, like MongoDB and CouchDB, also use JavaScript as their programming language.

A basic definition of JavaScript

JavaScript is a programming language that is:

• high level: it provides abstractions that allow you to ignore the details of the machine where it’s running on. It manages memory automatically with a garbage collector, so you can focus on the code instead of managing memory locations, and provides many constructs which allow you to deal with highly powerful variables and objects.
• dynamic: opposed to static programming languages, a dynamic language executes at runtime many of the things that a static language does at compile time. This has pros and cons, and it gives us powerful features like dynamic typing, late binding, reflection, functional programming, object runtime alteration, closures and much more.
• dynamically typed: a variable does not enforce a type. You can reassign any type to a variable, for example assigning an integer to a variable that holds a string.
• weakly typed: as opposed to strong typing, weakly (or loosely) typed languages do not enforce the type of an object, allowing more flexibility but denying us type safety and type checking (something that TypeScript and Flow aim to improve)
• interpreted: it’s commonly known as an interpreted language, which means that it does not need a compilation stage before a program can run, as opposed to C, Java or Go for example. In practice, browsers do compile JavaScript before executing it, for performance reasons, but this is transparent to you: there is no additional step involved.
• multi-paradigm: the language does not enforce any particular programming paradigm, unlike Java for example which forces the use of object oriented programming, or C that forces imperative programming. You can write JavaScript using an object-oriented paradigm, using prototypes and the new (as of ES6) classes syntax. You can write JavaScript in functional programming style, with its first class functions, or even in an imperative style (C-like).

In case you’re wondering, JavaScript has nothing to do with Java, it’s a poor name choice but we have to live with it.