According to mdn web docs -

We can all agree when I say that we are constantly connected with the web pages - it might be when you look for locations on map, watch video's or simply when you spend your time on social media feeds. In all these scenarios, we interact with our web pages right? We search for locations on maps, like and comment on social media, and play or pause videos. But what makes all these interactivity possible? The scripting/programming language JavaScript.

So, we understand that our little hero adds interactivity. Another important point to know about JavaScript is that it is currently the only computer language which allows us to directly interact with our web pages dynamically on the client. It's baked into the browser, which means JavaScript is already included, like a tool ready for use, allowing it to work on websites.

One of the reasons why it is so popular is because of its rules of backward compatibility. The rule states that all the websites built in the past should still work today. So removing JS from the browser would effectively render millions of websites completely useless.This very thing put javaScript in unique position of being one of the several central pillars of web development.

JavaScript unique ecosystem is one of the main reasons for its popularity. Simply put, browsers speak JavaScript. Also it is an easy language to get started with programming.

To summarise all the points I can say that a) JavaScript is a scripting language which adds interactivity to our web pages. b)it is one of its own kind which allows direct interaction with our web page c) It is backward compatible d)It is quite popular language and e) It is a easy language to get started in programming.