watch: use debounce instead of throttle

lib/internal/main/watch_mode.js

@@ -44,7 +44,7 @@ const args = ArrayPrototypeFilter(process.execArgv, (arg, i, arr) =>
   arg !== '--watch' && arg !== '--watch-preserve-output');
 ArrayPrototypePushApply(args, kCommand);
 
-const watcher = new FilesWatcher({ throttle: 500, mode: kShouldFilterModules ? 'filter' : 'all' });
+const watcher = new FilesWatcher({ debounce: 200, mode: kShouldFilterModules ? 'filter' : 'all' });
 ArrayPrototypeForEach(kWatchedPaths, (p) => watcher.watchPath(p));
 
 let graceTimer;

lib/internal/test_runner/runner.js

@@ -384,7 +384,7 @@ function runTestFile(path, root, inspectPort, filesWatcher, testNamePatterns) {
 function watchFiles(testFiles, root, inspectPort, signal, testNamePatterns) {
   const runningProcesses = new SafeMap();
   const runningSubtests = new SafeMap();
-  const watcher = new FilesWatcher({ throttle: 500, mode: 'filter', signal });
+  const watcher = new FilesWatcher({ debounce: 200, mode: 'filter', signal });
   const filesWatcher = { __proto__: null, watcher, runningProcesses, runningSubtests };
 
   watcher.on('changed', ({ owners }) => {

lib/internal/watch_mode/files_watcher.js

@@ -24,19 +24,19 @@ const supportsRecursiveWatching = process.platform === 'win32' ||
 class FilesWatcher extends EventEmitter {
   #watchers = new SafeMap();
   #filteredFiles = new SafeSet();
-  #throttling = new SafeSet();
+  #debouncing = new SafeSet();
   #depencencyOwners = new SafeMap();
   #ownerDependencies = new SafeMap();
-  #throttle;
+  #debounce;
   #mode;
   #signal;
 
-  constructor({ throttle = 500, mode = 'filter', signal } = kEmptyObject) {
+  constructor({ debounce = 200, mode = 'filter', signal } = kEmptyObject) {
     super();
 
-    validateNumber(throttle, 'options.throttle', 0, TIMEOUT_MAX);
+    validateNumber(debounce, 'options.debounce', 0, TIMEOUT_MAX);
     validateOneOf(mode, 'options.mode', ['filter', 'all']);
-    this.#throttle = throttle;
+    this.#debounce = debounce;
     this.#mode = mode;
     this.#signal = signal;
 
@@ -74,16 +74,18 @@ class FilesWatcher extends EventEmitter {
   }
 
   #onChange(trigger) {
-    if (this.#throttling.has(trigger)) {
+    if (this.#debouncing.has(trigger)) {
       return;
     }
     if (this.#mode === 'filter' && !this.#filteredFiles.has(trigger)) {
       return;
     }
-    this.#throttling.add(trigger);
+    this.#debouncing.add(trigger);
     const owners = this.#depencencyOwners.get(trigger);
-    this.emit('changed', { owners });
-    setTimeout(() => this.#throttling.delete(trigger), this.#throttle).unref();
+    setTimeout(() => {
+      this.#debouncing.delete(trigger);
+      this.emit('changed', { owners });
+    }, this.#debounce).unref();
   }
 
   get watchedPaths() {

test/parallel/test-watch-mode-files_watcher.mjs

@@ -26,7 +26,7 @@ describe('watch mode file watcher', () => {
 
   beforeEach(() => {
     changesCount = 0;
-    watcher = new FilesWatcher({ throttle: 100 });
+    watcher = new FilesWatcher({ debounce: 100 });
     watcher.on('changed', () => changesCount++);
   });
 
@@ -51,7 +51,7 @@ describe('watch mode file watcher', () => {
     assert.strictEqual(changesCount, 1);
   });
 
-  it('should throttle changes', async () => {
+  it('should debounce changes', async () => {
     const file = path.join(tmpdir.path, 'file2');
     writeFileSync(file, 'written');
     watcher.filterFile(file);
@@ -61,7 +61,7 @@ describe('watch mode file watcher', () => {
     writeFileSync(file, '2');
     writeFileSync(file, '3');
     writeFileSync(file, '4');
-    await setTimeout(200); // throttle * 2
+    await setTimeout(200); // debounce * 2
     writeFileSync(file, '5');
     const changed = once(watcher, 'changed');
     writeFileSync(file, 'after');
@@ -86,8 +86,8 @@ describe('watch mode file watcher', () => {
     await writeAndWaitForChanges(watcher, file);
 
     writeFileSync(file, '1');
+    assert.strictEqual(changesCount, 1);
 
-    await setTimeout(200); // avoid throttling
     watcher.clearFileFilters();
     writeFileSync(file, '2');
     // Wait for this long to make sure changes are triggered only once
@@ -97,7 +97,7 @@ describe('watch mode file watcher', () => {
 
   it('should watch all files in watched path when in "all" mode',
      { skip: !supportsRecursiveWatching }, async () => {
-       watcher = new FilesWatcher({ throttle: 100, mode: 'all' });
+       watcher = new FilesWatcher({ debounce: 100, mode: 'all' });
        watcher.on('changed', () => changesCount++);
 
        const file = path.join(tmpdir.path, 'file5');