https://wiki.openjdk.java.net/display/Nashorn/Main

fib.js

// Copyright (c) 2014, Ben Noordhuis <info@bnoordhuis.nl>
//
// Permission to use, copy, modify, and/or distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
// copyright notice and this permission notice appear in all copies.
//
// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
// ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
// ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
// OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

function fib(n) {
  return n > 1 ? fib(n - 1) + fib(n - 2) : n;
}
if (typeof print === 'undefined') {
  print = console.log;
}
print(fib(42));

nashorn.java

// Copyright (c) 2014, Ben Noordhuis <info@bnoordhuis.nl>
//
// Permission to use, copy, modify, and/or distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
// copyright notice and this permission notice appear in all copies.
//
// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
// ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
// ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
// OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.io.Reader;
import java.io.Writer;
import java.nio.charset.Charset;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.Paths;
import java.nio.ByteBuffer;
import javax.script.Invocable;
import javax.script.ScriptEngine;
import javax.script.ScriptEngineFactory;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;
import jdk.nashorn.api.scripting.NashornScriptEngineFactory;

class nashorn {
    public static void main(final String[] args) throws IOException {
        final ScriptEngineManager manager = new ScriptEngineManager();
        final NashornScriptEngineFactory factory = getScriptEngineFactory(manager);
        if (factory == null) {
            System.err.println("Nashorn script engine not found.  Wrong JDK?");
            System.exit(1);
        }

        // TODO(bnoordhuis) Parse Nashorn arguments and pass them to the engine.
        final ScriptEngine engine = factory.getScriptEngine(new String[] {});
        assert(engine != null);  // Sanity check, cannot really fail.

        if (args.length == 0) {
            repl(engine);
        } else {
            // TODO(bnoordhuis) Pass extra arguments to script.
            final Charset charset = Charset.forName("UTF-8");
            final String script = slurp(args[0], charset);
            final Object result = eval(engine, script);
            if (result instanceof ScriptException) {
                final ScriptException ex = (ScriptException) result;
                ex.printStackTrace(System.err);
                System.exit(1);
            }
        }
    }

    static void repl(final ScriptEngine engine) throws IOException {
        // TODO(bnoordhuis) Respect current locale.
        final Charset charset = Charset.forName("UTF-8");
        final Reader reader = new InputStreamReader(System.in, charset);
        final Writer writer = new OutputStreamWriter(System.out, charset);
        repl(engine, reader, writer);
    }

    static void repl(final ScriptEngine engine, final Reader in, final Writer out) throws IOException {
        final BufferedReader reader = new BufferedReader(in);
        final PrintWriter writer = new PrintWriter(out);
        while (true) {
            writer.print("> ");  
            writer.flush();
            final String line = reader.readLine();
            if (line == null) {  
                break;  // ^D
            }
            // TODO(bnoordhuis) Figure out how to discriminate between null and
            // undefined.  Nashorn currently returns null for both.
            final Object result = eval(engine, line);
            if (result != null) {
                writer.println(result);
                writer.flush();  
            }
        }
    }

    static Object eval(final ScriptEngine engine, final String script) {
        try {
            return engine.eval(script);
        } catch (ScriptException ex) {
            return ex;
        }
    }

    static String slurp(final String filename, final Charset charset) throws IOException {
        final Path path = Paths.get(filename);
        final byte[] bytes = Files.readAllBytes(path);
        final ByteBuffer buffer = ByteBuffer.wrap(bytes);
        return charset.decode(buffer).toString();
    }

    static NashornScriptEngineFactory getScriptEngineFactory(final ScriptEngineManager manager) {
        for (final ScriptEngineFactory factory : manager.getEngineFactories()) {
            if ("Oracle Nashorn".equals(factory.getEngineName()) &&
                factory instanceof NashornScriptEngineFactory) {
                return (NashornScriptEngineFactory) factory;
            }
        }
        return null;
    }
}

non-scientific-benchmark.txt

$ node -v
v0.10.25-pre

$ javac -version
javac 1.8.0-internal

# compile it
$ javac nashorn.java

# measure startup overhead
$ touch empty.js

# node startup overhead
$ perf stat -r10 node empty.js 2>&1 | grep 'seconds time elapsed'
       0.036602302 seconds time elapsed                                          ( +-  3.97% )

# nashorn/jvm startup overhead
$ perf stat -r10 java nashorn empty.js 2>&1 | grep 'seconds time elapsed'
       1.317808207 seconds time elapsed                                          ( +-  0.33% )

# node fib(42) performance
$ perf stat -r5 node fib.js 2>&1 | grep 'seconds time elapsed'
       5.377733374 seconds time elapsed                                          ( +-  0.36% )

# nashorn fib(42) performance
$ perf stat -r5 java nashorn fib.js 2>&1 | grep 'seconds time elapsed'
      10.303278074 seconds time elapsed                                          ( +-  2.22% )