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Nashorn: The New Rhino on the Block

3 min read

The most recent Java 8 release came with lots of new features, one of them is the brand-new JavaScript engine to replace the aging Rhino. This new engine, called Nashorn (German for rhinoceros), is high-performant and specification compliant. It is definitely useful whenever you want to mix-and-match your Java and JavaScript code.

To check the performance of Nashorn, I use it to run Esprima and let it parse some large code base (unminified jQuery, 268 KB). This quick, rather non-scientific test exercises two aspects of JavaScript run-time environment: continuous memory allocation (for the syntax nodes) and non-linear code execution (recursive-descent parsing).

If you want to follow along, check the repository Assuming you have JDK 8 installed properly, run the following:

javac -cp rhino.jar
java -cp .:rhino.jar speedtest

This test app will execute Esprima parser and tokenizer on the content of the test file. Rhino gets the first chance, Nashorn follows right after (each engine gets 30 runs). In the beginning, Rhino’s first run is 2607 ms and slowly it speeds up and finally this parsing is completed in just 824 ms. Nashorn timings have a different characteristic. When it is cold, Nashorn initially takes 5328 ms to carry out the operation but it quickly picks up the pace and before you know, it starts moving full steam ahead, reaching 208 ms per run.

Behind the scene, Nashorn compiles your JavaScript code into Java bytecodes and run them on the JVM itself. On top of that, Nashorn is taking advantage of invokedynamic instruction (from the Da Vinci Machine Project, part of Java 7) to permit “efficient and flexible execution” in a dynamic environment such as JavaScript. Other JVM languages, notably here JRuby, also benefit from this new invokedynamic feature.


What about Nashorn vs V8? It is not terribly fair to compare both, V8 is designed specifically for JavaScript while Nashorn leverages the battle-hardened, multi-language JVM. But for the fun of it, the Git repo also includes a JavaScript implementation of the test app which can be executed with V8 shell. On the same machine, V8 can complete the task in about 110 ms. Nashorn is not as mature as V8 yet, it is quite an achievement that it is only twice as slow as V8 for this specific test.

As a high-performance JavaScript on the JVM, Nashorn has many possible applications. It serves as a nice platform to play and experiment with JavaFX. Yet, it is powerful enough to be part of a web service stack (Vert.x, Project Avatar). On a less ambitious level, having another fast implementation of JavaScript is always good so that there is an alternative to run various JavaScript tools in an environment where Node.js is not available or not supported. As an illustration, check my previous blog post on a simple Ant task to validate JavaScript code.

Next time you have the urge to herd some rhinos, consider Nashorn!

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