You can use JavaScript anywhere

You can use JavaScript to write applications for web browsers, mobile devices, servers, desktops, Internet-of-Things devices, cloud functions, and really just about anywhere. Instead of having to use two, three, even four languages to build an application, developers can just use JavaScript. Having to learn and know only one language saves lots of time even if other languages are more effective on certain platforms than JavaScript.

JavaScript has a huge developer population

Lots and lots of developers use JavaScript. Anyone who programs for the Internet likely uses JavaScript at least a little bit, since JavaScript is almost required for the Internet (more on that later). A large developer population means people are actively making and supporting tools, resources, and improvements for JavaScript. You can know that if you choose JavaScript for your program the language will not be abandoned.

JavaScript is the programming language for web browsers

If you want to add interactivity and dynamic features to a web page, you pretty much have to use JavaScript. There are really no other programming languages or ways you can add interactivity to elements within a web page. Just about any web developer will probably know at least a little bit about JavaScript.

JavaScript is great for event-driven programming

Event-driven programming makes code that does something in response to an event, like when some bit of data finishes loading or the user clicks on a part of a web page. JavaScript was made from the ground up to do event-driven programming. Other programming languages have had to rely on complex tricks to simulate being event-driven. Event-driven programming in these languages can be very difficult and prone to bugs.

Companies large and small support JavaScript

The JavaScript ecosystem has strong and lasting support from all kinds of businesses and companies who use JavaScript to run their businesses and meet their customers needs. This means these companies have a direct investment in supporting and fostering the success of JavaScript and the tools they use. Like having a large developer population, having a large population of users using JavaScript in production helps make sure JavaScript will have continuing support and good health for a long time.