1 files changed, 111 insertions, 0 deletions
diff --git a/std/node/_fs/_fs_watch.ts b/std/node/_fs/_fs_watch.ts
new file mode 100644
index 000000000..a5f3bb9c1
--- /dev/null
+++ b/std/node/_fs/_fs_watch.ts
@@ -0,0 +1,111 @@
+import { fromFileUrl } from "../path.ts";
+import { EventEmitter } from "../events.ts";
+import { notImplemented } from "../_utils.ts";
+
+export function asyncIterableIteratorToCallback<T>(
+  iterator: AsyncIterableIterator<T>,
+  callback: (val: T, done?: boolean) => void,
+) {
+  function next() {
+    iterator.next().then((obj) => {
+      if (obj.done) {
+        callback(obj.value, true);
+        return;
+      }
+      callback(obj.value);
+      next();
+    });
+  }
+  next();
+}
+
+export function asyncIterableToCallback<T>(
+  iter: AsyncIterable<T>,
+  callback: (val: T, done?: boolean) => void,
+) {
+  const iterator = iter[Symbol.asyncIterator]();
+  function next() {
+    iterator.next().then((obj) => {
+      if (obj.done) {
+        callback(obj.value, true);
+        return;
+      }
+      callback(obj.value);
+      next();
+    });
+  }
+  next();
+}
+
+type watchOptions = {
+  persistent?: boolean;
+  recursive?: boolean;
+  encoding?: string;
+};
+
+type watchListener = (eventType: string, filename: string) => void;
+
+export function watch(
+  filename: string | URL,
+  options: watchOptions,
+  listener: watchListener,
+): FSWatcher;
+export function watch(
+  filename: string | URL,
+  listener: watchListener,
+): FSWatcher;
+export function watch(
+  filename: string | URL,
+  options: watchOptions,
+): FSWatcher;
+export function watch(filename: string | URL): FSWatcher;
+export function watch(
+  filename: string | URL,
+  optionsOrListener?: watchOptions | watchListener,
+  optionsOrListener2?: watchOptions | watchListener,
+) {
+  const listener = typeof optionsOrListener === "function"
+    ? optionsOrListener
+    : typeof optionsOrListener2 === "function"
+    ? optionsOrListener2
+    : undefined;
+  const options = typeof optionsOrListener === "object"
+    ? optionsOrListener
+    : typeof optionsOrListener2 === "object"
+    ? optionsOrListener2
+    : undefined;
+  filename = filename instanceof URL ? fromFileUrl(filename) : filename;
+
+  const iterator = Deno.watchFs(filename, {
+    recursive: options?.recursive || false,
+  });
+
+  if (!listener) throw new Error("No callback function supplied");
+
+  const fsWatcher = new FSWatcher(() => {
+    if (iterator.return) iterator.return();
+  });
+
+  fsWatcher.on("change", listener);
+
+  asyncIterableIteratorToCallback<Deno.FsEvent>(iterator, (val, done) => {
+    if (done) return;
+    fsWatcher.emit("change", val.kind, val.paths[0]);
+  });
+
+  return fsWatcher;
+}
+
+class FSWatcher extends EventEmitter {
+  close: () => void;
+  constructor(closer: () => void) {
+    super();
+    this.close = closer;
+  }
+  ref() {
+    notImplemented("FSWatcher.ref() is not implemented");
+  }
+  unref() {
+    notImplemented("FSWatcher.unref() is not implemented");
+  }
+}