Functionality for checking if external changes have occurred since the last time some code was run

[dsherret]

It might be neat to have an API that can be used to tell if some external changes have occurred since the last time a command was run. This would be useful for not doing an action if unnecessary to do so.

const tracker = $.changeTracker(import.meta, "data files"); // cache keyed on this current file and a string

tracker.addMtime("data/file1.json"); // hashes based on the file path's last modified time
tracker.addPath("data/file2.json"); // hashes based on the file path's content
tracker.addMtime("some_dir"); // hashes based on the descendants mtime
tracker.addPath("some_dir"); // hashes based on the descendants contents
tracker.addValue(123456); // hashes a specific value, which could have a source anywhere else

// multiple paths or values
tracker.addPaths(paths);
tracker.addMTimes(otherPaths);
tracker.addValues(values);

// will always run if the output path doesn't exist
tracker.addOutputPath("output/data.json");

// run if changed
if (tracker.hasChangedSync()) {
  await doStuff();
  tracker.commitSync();
}

// or as a single call
await tracker.runIfChanged(async () => {
  await doStuff();
});

// builder pattern
await $.changeTracker(import.meta, "data files")
  .addPaths(paths)
  .addOutputPath("output/data.json")
  .runIfChanged(async () => {
    await createOutputDataJsonFile();
  });

The hash could be saved in local storage.