Syntax is similar to C/C++ language making it easy to learn, but offers much more flexibility. Functions can be passed around asparameters and assigned to variables (like Lua), and allows programming asynchronous execution of functions.
There is a lot of development on the most widely used interpreters for this language, offering great performance; so good that you might get as surprised as I got while comparing the results with implementations in other languages.
Tests where run using node.js v5.7.1
$ time node jsrb.js real 0m1.755s user 0m0.156s sys 0m0.016s
Loading time is much slower than lua (and luajit).
$ time node jsrb.js real 8m49.170s user 8m40.620s sys 0m4.488s
Code metrics Line count: 250 code, 63 blank, 313 total File size: 6175 bytes
This is a good surprise; as can be seen, the arduous work of optimization done to Google's V8 Engine has really paid off.
No wonder why node.js is used as the backend for several websites and web services' APIs.
You can follow the development of this project on GitHub: https://github.com/niofis/raybench