Accept JS file as argument and support NPM modules via jvm-npm

- HelloNashorn now takes a JS file path as command-line argument
- Uses jvm-npm (org.bsc:jvm-npm-core:1.1.0) for require() support
- Require.root set to script's parent dir so node_modules resolves correctly
- Engine created with -scripting mode for load() support

build.gradle

@@ -9,6 +9,7 @@ repositories {
 
 dependencies {
     implementation 'org.openjdk.nashorn:nashorn-core:15.6'
+    implementation 'org.bsc:jvm-npm-core:1.1.0'
 }
 
 application {

src/main/java/com/example/HelloNashorn.java

@@ -3,18 +3,29 @@ package com.example;
 import org.openjdk.nashorn.api.scripting.NashornScriptEngineFactory;
 
 import javax.script.ScriptEngine;
+import java.io.File;
 
 public class HelloNashorn {
     public static void main(String[] args) throws Exception {
+        if (args.length == 0) {
+            System.err.println("Usage: HelloNashorn <script.js>");
+            System.exit(1);
+        }
+
+        File scriptFile = new File(args[0]).getAbsoluteFile();
+        if (!scriptFile.isFile()) {
+            System.err.println("File not found: " + args[0]);
+            System.exit(1);
+        }
+
         NashornScriptEngineFactory factory = new NashornScriptEngineFactory();
-        ScriptEngine engine = factory.getScriptEngine();
+        ScriptEngine engine = factory.getScriptEngine("-scripting");
 
-        engine.eval("print('Hello World from JavaScript!')");
+        engine.put("__rootDir", scriptFile.getParent());
+        engine.eval("load('classpath:jvm-npm.js')");
+        engine.eval("Require.root = __rootDir");
 
-        String result = (String) engine.eval(
-            "var greeting = 'Hello from Nashorn on JDK ' + java.lang.System.getProperty('java.version');" +
-            "greeting"
-        );
-        System.out.println(result);
+        engine.put("__scriptFile", scriptFile.getAbsolutePath());
+        engine.eval("load(__scriptFile)");
     }
 }