diff --git a/src/main/java/net/rptools/maptool/client/functions/MacroJavaScriptBridge.java b/src/main/java/net/rptools/maptool/client/functions/MacroJavaScriptBridge.java
index ffedf0e7ef..4bc84c9daa 100644
--- a/src/main/java/net/rptools/maptool/client/functions/MacroJavaScriptBridge.java
+++ b/src/main/java/net/rptools/maptool/client/functions/MacroJavaScriptBridge.java
@@ -26,6 +26,7 @@
 import net.rptools.maptool.client.MapTool;
 import net.rptools.maptool.client.MapToolVariableResolver;
 import net.rptools.maptool.client.script.javascript.JSArray;
+import net.rptools.maptool.client.script.javascript.JSContext;
 import net.rptools.maptool.client.script.javascript.JSObject;
 import net.rptools.maptool.client.script.javascript.JSScriptEngine;
 import net.rptools.maptool.client.script.javascript.api.MapToolJSAPIInterface;
@@ -52,13 +53,14 @@ public class MacroJavaScriptBridge extends AbstractFunction implements DefinesSp
 
   private MacroJavaScriptBridge() {
     super(
-        1,
+        0,
         UNLIMITED_PARAMETERS,
         "js.eval",
         "js.evalNS",
         "js.evalURI",
         "js.removeNS",
-        "js.createNS");
+        "js.createNS",
+        "js.listNS");
   }
 
   public static MacroJavaScriptBridge getInstance() {
@@ -72,6 +74,20 @@ public Object childEvaluate(
     variableResolver = (MapToolVariableResolver) resolver;
     String contextName = null;
 
+    if ("js.listNS".equalsIgnoreCase(functionName)) {
+      JsonArray array = new JsonArray();
+      JSScriptEngine.getContexts().stream()
+          .sorted(Comparator.comparing(JSContext::name))
+          .forEach(
+              c -> {
+                JsonObject obj = new JsonObject();
+                obj.addProperty("name", c.name());
+                obj.addProperty("trusted", c.trusted());
+                array.add(obj);
+              });
+      return array;
+    }
+
     if ("js.evalNS".equalsIgnoreCase(functionName) || "js.evalURI".equalsIgnoreCase(functionName)) {
       if (args.size() < 2) {
         throw new ParameterException(String.format(NOT_ENOUGH_PARAM, functionName, 2, args.size()));
@@ -80,11 +96,17 @@ public Object childEvaluate(
     }
 
     if ("js.removeNS".equalsIgnoreCase(functionName)) {
+      if (args.size() < 1) {
+        throw new ParameterException(String.format(NOT_ENOUGH_PARAM, functionName, 2, args.size()));
+      }
       contextName = (String) args.remove(0);
       JSScriptEngine.removeContext(contextName, MapTool.getParser().isMacroTrusted());
       return "removed";
     }
     if ("js.createNS".equalsIgnoreCase(functionName)) {
+      if (args.size() < 1) {
+        throw new ParameterException(String.format(NOT_ENOUGH_PARAM, functionName, 2, args.size()));
+      }
       contextName = (String) args.remove(0);
       boolean makeTrusted = MapTool.getParser().isMacroTrusted();
       if (args.size() > 0) {
@@ -97,6 +119,9 @@ public Object childEvaluate(
 
     String script;
     if ("js.evalURI".equalsIgnoreCase(functionName)) {
+      if (args.size() < 1) {
+        throw new ParameterException(String.format(NOT_ENOUGH_PARAM, functionName, 2, args.size()));
+      }
       URL url;
       try {
         url = new URL(args.get(0).toString());
diff --git a/src/main/java/net/rptools/maptool/client/script/javascript/JSContext.java b/src/main/java/net/rptools/maptool/client/script/javascript/JSContext.java
index cd60d861e9..418b0b49ed 100644
--- a/src/main/java/net/rptools/maptool/client/script/javascript/JSContext.java
+++ b/src/main/java/net/rptools/maptool/client/script/javascript/JSContext.java
@@ -20,14 +20,5 @@
 import org.graalvm.polyglot.*;
 import org.graalvm.polyglot.HostAccess.*;
 
-public class JSContext {
-  public boolean isTrusted;
-  public Context context;
-  public String name;
-
-  public JSContext(boolean t, Context c, String name) {
-    this.isTrusted = t;
-    this.context = c;
-    this.name = name;
-  }
-}
+public record JSContext(boolean trusted, Context context, String name) {}
+;
diff --git a/src/main/java/net/rptools/maptool/client/script/javascript/JSScriptEngine.java b/src/main/java/net/rptools/maptool/client/script/javascript/JSScriptEngine.java
index 7e0c74bef0..cd4f5890d7 100644
--- a/src/main/java/net/rptools/maptool/client/script/javascript/JSScriptEngine.java
+++ b/src/main/java/net/rptools/maptool/client/script/javascript/JSScriptEngine.java
@@ -35,6 +35,7 @@ public class JSScriptEngine {
   private static final JSScriptEngine jsScriptEngine = new JSScriptEngine();
   private static final Logger log = LogManager.getLogger(JSScriptEngine.class);
   private static final Map<String, JSContext> contexts = new HashMap<String, JSContext>();
+  private static final Map<String, JSContext> addOnContexts = new HashMap<String, JSContext>();
   private static final Stack<JSContext> contextStack = new Stack<>();
 
   public static JSContext getCurrentContext() {
@@ -42,10 +43,10 @@ public static JSContext getCurrentContext() {
   }
 
   public static boolean inTrustedContext() {
-    if (jsScriptEngine.contextStack.empty()) {
+    if (JSScriptEngine.contextStack.empty()) {
       return false;
     }
-    return jsScriptEngine.contextStack.peek().isTrusted;
+    return JSScriptEngine.contextStack.peek().trusted();
   }
 
   private void registerAPIObject(Value bindings, MapToolJSAPIInterface apiObj) {
@@ -91,7 +92,7 @@ public static void removeContext(String name, boolean trusted) throws ParserExce
       return;
     }
     JSContext c = contexts.get(name);
-    if (c == null || c.isTrusted) {
+    if (c == null || c.trusted()) {
       throw new ParserException(I18N.getText("macro.function.general.noPermJS", name));
     }
     contexts.remove(name);
@@ -101,6 +102,29 @@ public static void removeContext(String name, boolean trusted) throws ParserExce
   public static void resetContexts() {
     JSMacro.clear();
     contexts.clear();
+    addOnContexts.clear();
+  }
+
+  public static JSContext registerAddOnContext(String name) {
+    JSContext c = new JSContext(true, jsScriptEngine.makeContext(), name);
+    addOnContexts.put(name, c);
+    return c;
+  }
+
+  public static void removeAddOnContext(String name) {
+    addOnContexts.remove(name);
+  }
+
+  public static boolean hasContext(String name) {
+    return contexts.containsKey(name);
+  }
+
+  public static boolean hasAddOnContext(String name) {
+    return addOnContexts.containsKey(name);
+  }
+
+  public static Set<JSContext> getContexts() {
+    return new HashSet<>(contexts.values());
   }
 
   public Context makeContext() {
@@ -130,23 +154,37 @@ public static JSScriptEngine getJSScriptEngine() {
 
   public Value evalScript(String contextName, String script)
       throws ScriptException, ParserException {
+    return evalScript(contextName, script, MapTool.getParser().isMacroTrusted());
+  }
+
+  public Value evalScript(String contextName, String script, boolean trusted)
+      throws ScriptException, ParserException {
     if (contextName == null) {
       return evalAnonymous(script);
     }
     JSContext jc = contexts.get(contextName);
     if (jc == null) {
-      jc =
-          registerContext(
-              contextName,
-              MapTool.getParser().isMacroTrusted(),
-              MapTool.getParser().isMacroTrusted());
+      jc = registerContext(contextName, trusted, trusted);
     }
-    if (jc.isTrusted && !MapTool.getParser().isMacroTrusted()) {
-      throw new ParserException(I18N.getText("macro.function.general.noPermJS", contextName));
+
+    return evalScript(jc, script, trusted);
+  }
+
+  public Value evalAddOnScript(String contextName, String script, boolean trusted)
+      throws ScriptException, ParserException {
+    JSContext jc = addOnContexts.get(contextName);
+    return evalScript(jc, script, trusted);
+  }
+
+  public Value evalScript(JSContext context, String script, boolean trusted)
+      throws ScriptException, ParserException {
+
+    if (context.trusted() && !trusted) {
+      throw new ParserException(I18N.getText("macro.function.general.noPermJS", context.name()));
     }
-    contextStack.push(jc);
+    contextStack.push(context);
     try {
-      return jc.context.eval("js", script);
+      return context.context().eval("js", script);
     } finally {
       contextStack.pop();
     }
diff --git a/src/main/java/net/rptools/maptool/model/gamedata/data/AssetDataValue.java b/src/main/java/net/rptools/maptool/model/gamedata/data/AssetDataValue.java
index e5463135b0..d3f43d3299 100644
--- a/src/main/java/net/rptools/maptool/model/gamedata/data/AssetDataValue.java
+++ b/src/main/java/net/rptools/maptool/model/gamedata/data/AssetDataValue.java
@@ -107,7 +107,7 @@ public String asString() {
     if (undefined) {
       throw InvalidDataOperation.createUndefined(name);
     } else {
-      throw InvalidDataOperation.createInvalidConversion(DataType.ASSET, DataType.DOUBLE);
+      return asset.toString();
     }
   }
 
diff --git a/src/main/java/net/rptools/maptool/model/library/Library.java b/src/main/java/net/rptools/maptool/model/library/Library.java
index 6578802fac..0955686d60 100644
--- a/src/main/java/net/rptools/maptool/model/library/Library.java
+++ b/src/main/java/net/rptools/maptool/model/library/Library.java
@@ -203,4 +203,10 @@ public interface Library {
    * @return the {@link Asset} for the library license file if it has one.
    */
   CompletableFuture<Optional<Asset>> getLicenseAsset();
+
+  /**
+   * Clean up any resources used by the library, This should be called when the library is no longer
+   * needed.
+   */
+  void cleanup();
 }
diff --git a/src/main/java/net/rptools/maptool/model/library/addon/AddOnLibrary.java b/src/main/java/net/rptools/maptool/model/library/addon/AddOnLibrary.java
index 7e48410697..6907de90af 100644
--- a/src/main/java/net/rptools/maptool/model/library/addon/AddOnLibrary.java
+++ b/src/main/java/net/rptools/maptool/model/library/addon/AddOnLibrary.java
@@ -28,10 +28,12 @@
 import java.util.Optional;
 import java.util.Set;
 import java.util.concurrent.CompletableFuture;
+import javax.script.ScriptException;
 import net.rptools.lib.MD5Key;
 import net.rptools.maptool.client.MapTool;
 import net.rptools.maptool.client.MapToolMacroContext;
 import net.rptools.maptool.client.MapToolVariableResolver;
+import net.rptools.maptool.client.script.javascript.JSScriptEngine;
 import net.rptools.maptool.language.I18N;
 import net.rptools.maptool.model.Asset;
 import net.rptools.maptool.model.Asset.Type;
@@ -49,6 +51,7 @@
 import net.rptools.maptool.model.library.proto.AddOnLibraryEventsDto;
 import net.rptools.maptool.model.library.proto.MTScriptPropertiesDto;
 import net.rptools.maptool.util.threads.ThreadExecutionHelper;
+import net.rptools.parser.ParserException;
 import org.javatuples.Pair;
 
 /** Class that implements add-on libraries. */
@@ -60,6 +63,9 @@ public class AddOnLibrary implements Library {
   /** The name of the event for initialization. */
   private static final String INIT_EVENT = "onInit";
 
+  /** The prefix for the name of the JavaScript context for this addon. */
+  private static final String JS_CONTEXT_PREFIX = "addon:";
+
   /** Record used to store information about the MacrScript functions for this library. */
   private record MTScript(String path, boolean autoExecute, String description, MD5Key md5Key) {}
 
@@ -121,11 +127,17 @@ private record MTScript(String path, boolean autoExecute, String description, MD
   private final Map<String, String> legacyEventNameMap = new HashMap<>();
 
   /** The mapping between MTScript function paths and non legacy events. */
-  private final Map<String, String> eventNameMap = new HashMap<>();
+  private final Map<String, String> mtScriptEventNameMap = new HashMap<>();
+
+  /** The mapping between JavaScript script paths and non legacy events. */
+  private final Map<String, String> jsEventNameMap = new HashMap<>();
 
   /** The ID of the asset for the whole of the add-on Library. */
   private final MD5Key assetKey;
 
+  /** The name of the JavaScript context for the add on library. */
+  private final String jsContextName;
+
   /**
    * Class used to represent Drop In Libraries.
    *
@@ -172,7 +184,11 @@ private AddOnLibrary(
 
     eventsDto.getEventsList().stream()
         .filter(e -> !e.getMts().isEmpty())
-        .forEach(e -> eventNameMap.put(e.getName(), e.getMts()));
+        .forEach(e -> mtScriptEventNameMap.put(e.getName(), e.getMts()));
+
+    eventsDto.getEventsList().stream()
+        .filter(e -> !e.getJs().isEmpty())
+        .forEach(e -> jsEventNameMap.put(e.getName(), e.getJs()));
 
     eventsDto.getLegacyEventsList().stream()
         .filter(e -> !e.getMts().isEmpty())
@@ -201,6 +217,8 @@ private AddOnLibrary(
 
     licenseFile = dto.getLicenseFile();
     readMeFile = dto.getReadMeFile();
+
+    jsContextName = JS_CONTEXT_PREFIX + namespace;
   }
 
   /**
@@ -357,6 +375,14 @@ public CompletableFuture<Optional<Asset>> getLicenseAsset() {
     }
   }
 
+  @Override
+  public void cleanup() {
+    // Remove any existing JavaScript context if it exists
+    if (JSScriptEngine.hasAddOnContext(jsContextName)) {
+      JSScriptEngine.removeAddOnContext(jsContextName);
+    }
+  }
+
   @Override
   public CompletableFuture<String> getVersion() {
     return CompletableFuture.completedFuture(version);
@@ -485,14 +511,27 @@ void initialize() {
                         data.needsInitialization()
                             .thenAccept(
                                 needInit -> {
+                                  // First remove any existing JavaScript context if it exists
+                                  if (JSScriptEngine.hasAddOnContext(jsContextName)) {
+                                    JSScriptEngine.removeAddOnContext(jsContextName);
+                                  }
+                                  // Then create a new JavaScript context for the add-on library
+                                  JSScriptEngine.registerAddOnContext(jsContextName);
                                   if (needInit) {
-                                    if (eventNameMap.containsKey(FIRST_INIT_EVENT)) {
-                                      callMTSFunction(eventNameMap.get(FIRST_INIT_EVENT)).join();
+                                    if (jsEventNameMap.containsKey(FIRST_INIT_EVENT)) {
+                                      runJS(jsEventNameMap.get(FIRST_INIT_EVENT));
+                                    }
+                                    if (mtScriptEventNameMap.containsKey(FIRST_INIT_EVENT)) {
+                                      callMTSFunction(mtScriptEventNameMap.get(FIRST_INIT_EVENT))
+                                          .join();
                                       data.setNeedsToBeInitialized(false).join();
                                     }
                                   }
-                                  if (eventNameMap.containsKey(INIT_EVENT)) {
-                                    callMTSFunction(eventNameMap.get(INIT_EVENT)).join();
+                                  if (jsEventNameMap.containsKey(INIT_EVENT)) {
+                                    runJS(jsEventNameMap.get(INIT_EVENT));
+                                  }
+                                  if (mtScriptEventNameMap.containsKey(INIT_EVENT)) {
+                                    callMTSFunction(mtScriptEventNameMap.get(INIT_EVENT)).join();
                                   }
                                 });
                       });
@@ -516,6 +555,26 @@ private CompletableFuture<Void> callMTSFunction(String name) {
             });
   }
 
+  /**
+   * Run the specified JavaScript code from the add-on library in the add-on library's JavaScript
+   * context.
+   *
+   * @param file the JavaScript file withing the file to run.
+   */
+  private void runJS(String file) {
+    readFile(file)
+        .thenAccept(
+            script -> {
+              try {
+                JSScriptEngine.getJSScriptEngine()
+                    .evalScript(jsContextName, script.asAsset().getDataAsString(), true);
+              } catch (ParserException | ScriptException e) {
+                throw new RuntimeException(e);
+              }
+            })
+        .join();
+  }
+
   CompletableFuture<DataValue> readFile(String path) {
     return CompletableFuture.supplyAsync(
         () -> {
diff --git a/src/main/java/net/rptools/maptool/model/library/addon/AddOnLibraryManager.java b/src/main/java/net/rptools/maptool/model/library/addon/AddOnLibraryManager.java
index b462d21558..5d04309356 100644
--- a/src/main/java/net/rptools/maptool/model/library/addon/AddOnLibraryManager.java
+++ b/src/main/java/net/rptools/maptool/model/library/addon/AddOnLibraryManager.java
@@ -93,6 +93,7 @@ public void registerLibrary(AddOnLibrary library) {
   public void deregisterLibrary(String namespace) {
     var removed = namespaceLibraryMap.remove(namespace.toLowerCase());
     if (removed != null) {
+      removed.cleanup();
       new MapToolEventBus()
           .getMainEventBus()
           .post(new AddOnsRemovedEvent(Set.of(removed.getLibraryInfo().join())));
@@ -172,6 +173,9 @@ public void removeAllLibraries() {
 
     if (libs.size() > 0) {
       new MapToolEventBus().getMainEventBus().post(new AddOnsRemovedEvent(libs));
+      for (var library : namespaceLibraryMap.values()) {
+        library.cleanup();
+      }
       namespaceLibraryMap.clear();
     }
   }
diff --git a/src/main/java/net/rptools/maptool/model/library/token/LibraryToken.java b/src/main/java/net/rptools/maptool/model/library/token/LibraryToken.java
index a4bb9bc1c1..1cfa5ee972 100644
--- a/src/main/java/net/rptools/maptool/model/library/token/LibraryToken.java
+++ b/src/main/java/net/rptools/maptool/model/library/token/LibraryToken.java
@@ -363,6 +363,11 @@ public CompletableFuture<Optional<Asset>> getLicenseAsset() {
     return CompletableFuture.completedFuture(Optional.empty());
   }
 
+  @Override
+  public void cleanup() {
+    // No cleanup needed
+  }
+
   /**
    * @param id the id of the token Lib:Token to get.
    * @return the Token for the library.