Relative handling, import.meta.url encouragement

README.md

@@ -33,7 +33,7 @@ _Here's how this is different from worker_threads:_
 ```js
 import Worker from 'web-worker';
 
-const worker = new Worker('./worker.js');
+const worker = new Worker(new URL('./worker.js', import.meta.url));
 
 worker.addEventListener('message', e => {
   console.log(e.data)  // "hiya!"
@@ -55,6 +55,9 @@ addEventListener('message', e => {
 </td></tr></tbody>
 </table>
 
+The pattern `new URL('./worker.js', import.meta.url)` is used above to load the worker relative to the current module instead of the application base URL. Without this, Worker URLs are relative to a document's URL, which in Node.js is interpreted to be `process.cwd()`.
+
+Support for this pattern in build tools and test frameworks is still quite limited, but we are working on growing this support (tracking issue https://github.com/developit/web-worker/issues/4).
 
 ### Module Workers
 
@@ -68,7 +71,7 @@ In the browser, they can be used natively in Chrome 80+, or in all browsers via
 ```js
 import Worker from 'web-worker';
 
-const worker = new Worker('./worker.mjs', {
+const worker = new Worker(new URL('./worker.mjs', import.meta.url), {
   type: 'module'
 });
 worker.addEventListener('message', e => {

node.js

@@ -72,6 +72,8 @@ function Event(type, target) {
 // thread boundary, but behaves differently in each context.
 export default threads.isMainThread ? mainThread() : workerThread();
 
+const baseUrl = URL.pathToFileURL(process.cwd() + '/');
+
 function mainThread() {
 
 	/**
@@ -90,15 +92,13 @@ function mainThread() {
 		constructor(url, options) {
 			super();
 			const { name, type } = options || {};
-			// hack: grab the caller's filename from a stack trace
-			let relativeTo = process.cwd();
-			try {
-				relativeTo = Error().stack.split('\n')[2].match(/ \((.+):[^:]+:[^:]+\)$/)[1];
+			if (typeof url !== 'string') url = url.toString();
+			let mod;
+			if (/^data:/.test(url)) {
+				mod = url;
 			}
-			catch (e) {}
-			let mod = url;
-			if (!/^data:/.test(url)) {
-				mod = URL.fileURLToPath(new URL.URL(url, 'file://' + relativeTo));
+			else {
+				mod = URL.fileURLToPath(new URL.URL(url, baseUrl));
 			}
 			const worker = new threads.Worker(
 				__filename,

test/index.test.js

@@ -35,7 +35,7 @@ test.after.always(t => {
 });
 
 test.serial('instantiation', async t => {
-	worker = createModuleWorker('./fixtures/worker.mjs');
+	worker = createModuleWorker('./test/fixtures/worker.mjs');
 	await sleep(500);
 	t.is(worker.events.length, 1, 'should have received a message event');
 	t.is(worker.events[0].data, 42);