Many companies that are dedicated to developing software, mobile apps and web design based their products in JS.
What is JS?
JS is a programming language for web development.
Along HTML (Markup language) and CSS (Style rules), are the tools every Frontend developer must learn.
History (short version)
It was first released in 1995 as part of Netscape. In 1996 it was submitted to ECMA international. It has traveled a long road towards standardization. This was completely achieved only in ECMAScript 5 standard, released in December 2009.
What is JS used for?
Frontend: JS with HTML and CSS are the default tools for developing client-side websites.
Backend: with server-side frameworks, like NodeJs, JS works for backend developments. This means that JS is a full stack programming language.
Mobile apps: JS can be used for developing mobile apps, however, they don’t run natively neither on iOS or Android
Web apps: There are plenty of frameworks for maximizing JS for these purposes. Examples of these are React, Angular, and others.