One of the most important tools you will be using as a programmer is the programming language. Seems obvious, right? But it’s worth saying that.
The more in-depth knowledge you have about the language you use, the more productive and efficient you are.
From a small utility language that ran inside browsers, it has expanded to broad server usage with Node.js, and it’s also used on mobile and desktop apps with great success.
I think it’s great to learn more than one language, too. A language defines its own little world. Knowing more languages lets you be more wise with your choices, and know more little worlds.