If you are using Maven or Gradle, add the following dependency to the _dependencies_ section of your
project descriptor to access the Vert.x Core API and enable the JavaScript support:

* Maven (in your `pom.xml`):

[source,xml,subs="+attributes"]
----
<dependency>
 <groupId>io.vertx</groupId>
 <artifactId>vertx-core</artifactId>
 <version>3.4.2</version>
</dependency>
<dependency>
  <groupId>io.vertx</groupId>
  <artifactId>vertx-lang-js</artifactId>
  <version>3.4.2</version>
</dependency>
----

* Gradle (in your `build.gradle` file):

[source,groovy,subs="+attributes"]
----
compile "io.vertx:vertx-core:3.4.2"
compile "io.vertx:vertx-lang-js:3.4.2"
----

[IMPORTANT]
====
The JavaScript support is based on http://openjdk.java.net/projects/nashorn/[Nashorn], and so is
constrained by Nashorn feature set and limits.

It does not support EcmaScript 6, because Nashorn does not support it.

In addition, _native_ NPM modules cannot be used as they are _compiled_ for Node.JS. NPMs developed in EcmaScript 6
are also not usable.
====