Chapter 12. Nashorn

With Java 8, Oracle has included Nashorn, a new JavaScript implementation that runs on the JVM. Nashorn is designed to replace the original JavaScript-on-the-JVM project—which was called Rhino (Nashorn is the German word for “rhino”).

Nashorn is a completely rewritten implementation and strives for easy interoperability with Java, high performance, and precise conformance to the JavaScript ECMA specifications. Nashorn was the first implementation of JavaScript to hit a perfect 100% on spec compliance and is already at least 20 times faster than Rhino on most workloads.

Introduction to Nashorn

In this chapter, we will assume some basic understanding of JavaScript. If you aren’t already familiar with basic JavaScript concepts, then Head First JavaScript by Michael Morrison (O’Reilly) is a good place to start.

If you recall the differences between Java and JavaScript outlined in “Java Compared to JavaScript”, you know that we can see that the two languages are very different. It may, therefore, seem surprising that JavaScript should be able to run on top of the same virtual machine as Java.

Non-Java Languages on the JVM

In fact, there are a very large number of non-Java languages that run on the JVM—and some of them are a lot more unlike Java than JavaScript is. This is made possible by the fact that the Java language and JVM are only very loosely coupled, and only really interact via the definition of the class file format. This can be accomplished in two different ...

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