CLI Options in Node.js¶

Node.js comes with a variety of CLI options. These options expose built-in debugging, multiple ways to execute scripts, and other helpful runtime options.

In this tutorial, we are going to learn how to specify CLI options in Javet.

In Node.js the CLI options consists of the following:

Options - NodeFlags
V8 options - V8Flags
Arguments - NodeRuntimeOptions

node [options] [V8 options] [<program-entry-point> | -e "script" | -] [--] [arguments]

Options¶

Options are often used to turn on some Node.js specific features. Let's take Temporal for instance.

Temporal is a stage-3 TC39 proposal exposed in Node.js behind --harmony-temporal. Let's see how to enable it in Javet.

Step 1: Set Options¶

Execute the following Java code before the first NodeRuntime is created.

NodeRuntimeOptions.NODE_FLAGS.setHarmonyTemporal(true);

Step 2: Let's Go¶

Run the following JavaScript code.

console.log(Temporal.Now.instant().toString());

It works!

2026-05-03T12:34:56.789Z

Note

NodeRuntimeOptions.NODE_FLAGS is a global config that applies to all the Node.js runtimes. Once the first Node.js runtime is initialized, NodeRuntimeOptions.NODE_FLAGS is sealed and no longer accepts further changes.

More Options¶

There are more options available in NodeFlags, e.g. --allow-fs-read, --allow-fs-write, --no-warnings. And NodeFlags also support custom flags.

Arguments¶

The arguments can be set as follows. It can be specified per Node.js runtime creation.

NodeRuntimeOptions nodeRuntimeOptions = new NodeRuntimeOptions();
nodeRuntimeOptions.setConsoleArguments(new String[]{"--abc", "--def"});
try (NodeRuntime testNodeRuntime = v8Host.createV8Runtime(nodeRuntimeOptions)) {
    List<String> consoleArguments = testNodeRuntime.getExecutor("process.argv;").executeObject();
    assertEquals(3, consoleArguments.size());
    assertEquals("--abc", consoleArguments.get(1));
    assertEquals("--def", consoleArguments.get(2));
}