ERROR - [JSC_UNDEFINED_VARIABLE] variable process is undeclared

[faveoled]

Trying to write a binding for Node's process.hrtime() in J2CL:

@JsType(isNative = true, name="process", namespace = GLOBAL)
public class Process {

    @JsMethod(name="hrtime")
    public static native JsArray<Integer> hrtime();

}

Getting this error:

[ERROR] app:app:1.0-SNAPSHOT/optimized_js: /home/user/Dev/Java/j2cl-node/target/gwt3BuildCache/0.20/app-app-1.0-SNAPSHOT/446a7868cb65e18b39fa3d8a66e00ec8-transpiled_js/results/app/Process$$Overlay.impl.java.js:15:29: ERROR - [JSC_UNDEFINED_VARIABLE] variable process is undeclared
  return instance instanceof process;
                             ^^^^^^^

[INFO] app:app:1.0-SNAPSHOT/optimized_js: 1 error(s), 0 warning(s)

[ERROR] Exception executing task app:app:1.0-SNAPSHOT/optimized_js
java.lang.IllegalStateException: Closure Compiler failed, check log for details
    at com.vertispan.j2cl.build.provided.ClosureTask$4.execute (ClosureTask.java:265)
    at com.vertispan.j2cl.build.TaskScheduler$2.executeTask (TaskScheduler.java:214)
    at com.vertispan.j2cl.build.TaskScheduler$2.lambda$onReady$0 (TaskScheduler.java:266)
    at java.util.concurrent.Executors$RunnableAdapter.call (Executors.java:515)
    at java.util.concurrent.FutureTask.run (FutureTask.java:264)
    at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run (ScheduledThreadPoolExecutor.java:304)
    at java.util.concurrent.ThreadPoolExecutor.runWorker (ThreadPoolExecutor.java:1128)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run (ThreadPoolExecutor.java:628)
    at java.lang.Thread.run (Thread.java:829)
java.lang.RuntimeException
        at com.vertispan.j2cl.build.DiskCache.markFailed(DiskCache.java:542)
        at com.vertispan.j2cl.build.DiskCache$CacheResult.markFailure(DiskCache.java:62)
        at com.vertispan.j2cl.build.TaskScheduler$2.executeTask(TaskScheduler.java:235)
        at com.vertispan.j2cl.build.TaskScheduler$2.lambda$onReady$0(TaskScheduler.java:266)
        at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515)
        at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
        at java.base/java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:304)
        at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
        at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
        at java.base/java.lang.Thread.run(Thread.java:829)

Any ideas?

[niloc132]

Unfortunately, defining a JsType is only part of the process - this only tells j2cl what the type is, and how to accurately generate references to it from other types (plus also how to work out constants, some helper methods, etc).

The other part of the puzzle you need is to give the closure compiler the externs for the type. See https://developers.google.com/closure/compiler/docs/externs-and-exports for a quick summary, and https://github.com/google/closure-compiler/tree/master/contrib/externs for some other example files.

In your case, add a js file to the project that looks something like this:

/**
 * @externs 
 */

function process() {}

/**
 * @returns number[]
 */
process.hrtime = function(){};

I'm not quite sure if this is actually accurate for your purposes, but it seems to reflect the Java you've declared. For example there is a constructor for process, but no members, just a single static function.

When naming this file, we are encouraging a .externs.js extension in the src/main/java or src/main/resources directory, or if you want to only name it as .js, consider putting it in the META-INF/externs/ of the jar (so, probably within src/main/resources). Technically a plain .js file in your source directory will work today too, but it might make some future enhancements trickier to implement.

j2clmavenplugin/j2cl-tasks/src/main/java/com/vertispan/j2cl/build/provided/ClosureTask.java

Lines 44 to 54 in d90ded0

	public static final PathMatcher EXTERNS = new PathMatcher() {
	@Override
	public boolean matches(Path path) {
	return IN_META_INF_EXTERNS.matches(path) || EXTERNS_SOURCES.matches(path);
	}
	@Override
	public String toString() {
	return "externs to pass to closure";
	}
	};

Personally I would suggest putting it in the same package as the Process.java file above, so that if you update one, you know to also update the other.

[faveoled]

Thanks, it worked