---
title: Watch filesystem changes
description: Monitor files and directories in real-time to build responsive development tools and automation workflows.
image: https://developers.cloudflare.com/dev-products-preview.png
---

> Documentation Index  
> Fetch the complete documentation index at: https://developers.cloudflare.com/sandbox/llms.txt  
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# Watch filesystem changes

This guide shows you how to monitor filesystem changes in real-time using the Sandbox SDK's file watching API. File watching is useful for building development tools, automated workflows, and applications that react to file changes as they happen.

The `watch()` method returns an SSE (Server-Sent Events) stream that you consume with `parseSSEStream()`. Each event in the stream describes a filesystem change.

## Basic file watching

Start by watching a directory for any changes:

* [  JavaScript ](#tab-panel-10770)
* [  TypeScript ](#tab-panel-10771)

JavaScript

```
import { parseSSEStream } from "@cloudflare/sandbox";
const stream = await sandbox.watch("/workspace/src");
for await (const event of parseSSEStream(stream)) {  if (event.type === "event") {    console.log(`${event.eventType}: ${event.path}`);    console.log(`Is directory: ${event.isDirectory}`);  }}
```

TypeScript

```
import { parseSSEStream } from "@cloudflare/sandbox";import type { FileWatchSSEEvent } from "@cloudflare/sandbox";
const stream = await sandbox.watch("/workspace/src");
for await (const event of parseSSEStream<FileWatchSSEEvent>(stream)) {  if (event.type === "event") {    console.log(`${event.eventType}: ${event.path}`);    console.log(`Is directory: ${event.isDirectory}`);  }}
```

The stream emits four lifecycle event types:

* **`watching`** — Watch established, includes the `watchId`
* **`event`** — A filesystem change occurred
* **`error`** — The watch encountered an error
* **`stopped`** — The watch was stopped

Filesystem change events (`event.eventType`) include:

* **`create`** — File or directory was created
* **`modify`** — File content changed
* **`delete`** — File or directory was removed
* **`move_from`** / **`move_to`** — File or directory was moved or renamed
* **`attrib`** — File attributes changed (permissions, timestamps)

## Filter by file type

Use `include` patterns to watch only specific file types:

* [  JavaScript ](#tab-panel-10772)
* [  TypeScript ](#tab-panel-10773)

JavaScript

```
import { parseSSEStream } from "@cloudflare/sandbox";
// Only watch TypeScript and JavaScript filesconst stream = await sandbox.watch("/workspace/src", {  include: ["*.ts", "*.tsx", "*.js", "*.jsx"],});
for await (const event of parseSSEStream(stream)) {  if (event.type === "event") {    console.log(`${event.eventType}: ${event.path}`);  }}
```

TypeScript

```
import { parseSSEStream } from "@cloudflare/sandbox";import type { FileWatchSSEEvent } from "@cloudflare/sandbox";
// Only watch TypeScript and JavaScript filesconst stream = await sandbox.watch("/workspace/src", {  include: ["*.ts", "*.tsx", "*.js", "*.jsx"],});
for await (const event of parseSSEStream<FileWatchSSEEvent>(stream)) {  if (event.type === "event") {    console.log(`${event.eventType}: ${event.path}`);  }}
```

Common include patterns:

* `*.ts` — TypeScript files
* `*.js` — JavaScript files
* `*.json` — JSON configuration files
* `*.md` — Markdown documentation
* `package*.json` — Package files specifically

## Exclude directories

Use `exclude` patterns to skip certain directories or files:

* [  JavaScript ](#tab-panel-10774)
* [  TypeScript ](#tab-panel-10775)

JavaScript

```
import { parseSSEStream } from "@cloudflare/sandbox";
const stream = await sandbox.watch("/workspace", {  exclude: ["node_modules", "dist", "*.log", ".git", "*.tmp"],});
for await (const event of parseSSEStream(stream)) {  if (event.type === "event") {    console.log(`Change detected: ${event.path}`);  }}
```

TypeScript

```
import { parseSSEStream } from "@cloudflare/sandbox";import type { FileWatchSSEEvent } from "@cloudflare/sandbox";
const stream = await sandbox.watch("/workspace", {  exclude: ["node_modules", "dist", "*.log", ".git", "*.tmp"],});
for await (const event of parseSSEStream<FileWatchSSEEvent>(stream)) {  if (event.type === "event") {    console.log(`Change detected: ${event.path}`);  }}
```

Default exclusions

The following patterns are excluded by default: `.git`, `node_modules`, `.DS_Store`. You can override this by providing your own `exclude` array.

## Build responsive development tools

### Auto-rebuild on changes

Trigger builds automatically when source files are modified:

* [  JavaScript ](#tab-panel-10786)
* [  TypeScript ](#tab-panel-10787)

JavaScript

```
import { parseSSEStream } from "@cloudflare/sandbox";
const stream = await sandbox.watch("/workspace/src", {  include: ["*.ts", "*.tsx"],});
let buildInProgress = false;
for await (const event of parseSSEStream(stream)) {  if (    event.type === "event" &&    event.eventType === "modify" &&    !buildInProgress  ) {    buildInProgress = true;    console.log(`File changed: ${event.path}, rebuilding...`);
    try {      const result = await sandbox.exec("npm run build");      if (result.success) {        console.log("Build completed successfully");      } else {        console.error("Build failed:", result.stderr);      }    } catch (error) {      console.error("Build error:", error);    } finally {      buildInProgress = false;    }  }}
```

TypeScript

```
import { parseSSEStream } from "@cloudflare/sandbox";import type { FileWatchSSEEvent } from "@cloudflare/sandbox";
const stream = await sandbox.watch("/workspace/src", {  include: ["*.ts", "*.tsx"],});
let buildInProgress = false;
for await (const event of parseSSEStream<FileWatchSSEEvent>(stream)) {  if (    event.type === "event" &&    event.eventType === "modify" &&    !buildInProgress  ) {    buildInProgress = true;    console.log(`File changed: ${event.path}, rebuilding...`);
    try {      const result = await sandbox.exec("npm run build");      if (result.success) {        console.log("Build completed successfully");      } else {        console.error("Build failed:", result.stderr);      }    } catch (error) {      console.error("Build error:", error);    } finally {      buildInProgress = false;    }  }}
```

### Auto-run tests on change

Re-run tests when test files are modified:

* [  JavaScript ](#tab-panel-10776)
* [  TypeScript ](#tab-panel-10777)

JavaScript

```
import { parseSSEStream } from "@cloudflare/sandbox";
const stream = await sandbox.watch("/workspace/tests", {  include: ["*.test.ts", "*.spec.ts"],});
for await (const event of parseSSEStream(stream)) {  if (event.type === "event" && event.eventType === "modify") {    console.log(`Test file changed: ${event.path}`);    const result = await sandbox.exec(`npm test -- ${event.path}`);    console.log(result.success ? "Tests passed" : "Tests failed");  }}
```

TypeScript

```
import { parseSSEStream } from "@cloudflare/sandbox";import type { FileWatchSSEEvent } from "@cloudflare/sandbox";
const stream = await sandbox.watch("/workspace/tests", {  include: ["*.test.ts", "*.spec.ts"],});
for await (const event of parseSSEStream<FileWatchSSEEvent>(stream)) {  if (event.type === "event" && event.eventType === "modify") {    console.log(`Test file changed: ${event.path}`);    const result = await sandbox.exec(`npm test -- ${event.path}`);    console.log(result.success ? "Tests passed" : "Tests failed");  }}
```

### Incremental indexing

Re-index only changed files instead of rescanning an entire directory tree:

* [  JavaScript ](#tab-panel-10780)
* [  TypeScript ](#tab-panel-10781)

JavaScript

```
import { parseSSEStream } from "@cloudflare/sandbox";
const stream = await sandbox.watch("/workspace/docs", {  include: ["*.md", "*.mdx"],});
for await (const event of parseSSEStream(stream)) {  if (event.type === "event") {    switch (event.eventType) {      case "create":      case "modify":        console.log(`Indexing ${event.path}...`);        await indexFile(event.path);        break;      case "delete":        console.log(`Removing ${event.path} from index...`);        await removeFromIndex(event.path);        break;    }  }}
```

TypeScript

```
import { parseSSEStream } from "@cloudflare/sandbox";import type { FileWatchSSEEvent } from "@cloudflare/sandbox";
const stream = await sandbox.watch("/workspace/docs", {  include: ["*.md", "*.mdx"],});
for await (const event of parseSSEStream<FileWatchSSEEvent>(stream)) {  if (event.type === "event") {    switch (event.eventType) {      case "create":      case "modify":        console.log(`Indexing ${event.path}...`);        await indexFile(event.path);        break;      case "delete":        console.log(`Removing ${event.path} from index...`);        await removeFromIndex(event.path);        break;    }  }}
```

## Advanced patterns

### Process events with a helper function

Extract event processing into a reusable function that handles stream lifecycle:

* [  JavaScript ](#tab-panel-10796)
* [  TypeScript ](#tab-panel-10797)

JavaScript

```
import { parseSSEStream } from "@cloudflare/sandbox";
async function watchFiles(sandbox, path, options, handler) {  const stream = await sandbox.watch(path, options);
  for await (const event of parseSSEStream(stream)) {    switch (event.type) {      case "watching":        console.log(`Watching ${event.path}`);        break;      case "event":        await handler(event.eventType, event.path, event.isDirectory);        break;      case "error":        console.error(`Watch error: ${event.error}`);        break;      case "stopped":        console.log(`Watch stopped: ${event.reason}`);        return;    }  }}
// Usageawait watchFiles(  sandbox,  "/workspace/src",  { include: ["*.ts"] },  async (eventType, filePath) => {    console.log(`${eventType}: ${filePath}`);  },);
```

TypeScript

```
import { parseSSEStream } from "@cloudflare/sandbox";import type { FileWatchSSEEvent } from "@cloudflare/sandbox";
async function watchFiles(  sandbox: any,  path: string,  options: { include?: string[]; exclude?: string[] },  handler: (    eventType: string,    filePath: string,    isDirectory: boolean,  ) => Promise<void>,) {  const stream = await sandbox.watch(path, options);
  for await (const event of parseSSEStream<FileWatchSSEEvent>(stream)) {    switch (event.type) {      case "watching":        console.log(`Watching ${event.path}`);        break;      case "event":        await handler(event.eventType, event.path, event.isDirectory);        break;      case "error":        console.error(`Watch error: ${event.error}`);        break;      case "stopped":        console.log(`Watch stopped: ${event.reason}`);        return;    }  }}
// Usageawait watchFiles(  sandbox,  "/workspace/src",  { include: ["*.ts"] },  async (eventType, filePath) => {    console.log(`${eventType}: ${filePath}`);  },);
```

### Debounced file operations

Avoid excessive operations by collecting changes before processing:

* [  JavaScript ](#tab-panel-10790)
* [  TypeScript ](#tab-panel-10791)

JavaScript

```
import { parseSSEStream } from "@cloudflare/sandbox";
const stream = await sandbox.watch("/workspace/src");const changedFiles = new Set();let debounceTimeout = null;
for await (const event of parseSSEStream(stream)) {  if (event.type === "event") {    changedFiles.add(event.path);
    if (debounceTimeout) {      clearTimeout(debounceTimeout);    }
    debounceTimeout = setTimeout(async () => {      console.log(`Processing ${changedFiles.size} changed files...`);      for (const filePath of changedFiles) {        await processFile(filePath);      }      changedFiles.clear();      debounceTimeout = null;    }, 1000);  }}
```

TypeScript

```
import { parseSSEStream } from "@cloudflare/sandbox";import type { FileWatchSSEEvent } from "@cloudflare/sandbox";
const stream = await sandbox.watch("/workspace/src");const changedFiles = new Set<string>();let debounceTimeout: ReturnType<typeof setTimeout> | null = null;
for await (const event of parseSSEStream<FileWatchSSEEvent>(stream)) {  if (event.type === "event") {    changedFiles.add(event.path);
    if (debounceTimeout) {      clearTimeout(debounceTimeout);    }
    debounceTimeout = setTimeout(async () => {      console.log(`Processing ${changedFiles.size} changed files...`);      for (const filePath of changedFiles) {        await processFile(filePath);      }      changedFiles.clear();      debounceTimeout = null;    }, 1000);  }}
```

### Watch with non-recursive mode

Watch only the top level of a directory, without descending into subdirectories:

* [  JavaScript ](#tab-panel-10778)
* [  TypeScript ](#tab-panel-10779)

JavaScript

```
import { parseSSEStream } from "@cloudflare/sandbox";
// Only watch root-level config filesconst stream = await sandbox.watch("/workspace", {  include: ["package.json", "tsconfig.json", "vite.config.ts"],  recursive: false,});
for await (const event of parseSSEStream(stream)) {  if (event.type === "event") {    console.log("Configuration changed, rebuilding project...");    await sandbox.exec("npm run build");  }}
```

TypeScript

```
import { parseSSEStream } from "@cloudflare/sandbox";import type { FileWatchSSEEvent } from "@cloudflare/sandbox";
// Only watch root-level config filesconst stream = await sandbox.watch("/workspace", {  include: ["package.json", "tsconfig.json", "vite.config.ts"],  recursive: false,});
for await (const event of parseSSEStream<FileWatchSSEEvent>(stream)) {  if (event.type === "event") {    console.log("Configuration changed, rebuilding project...");    await sandbox.exec("npm run build");  }}
```

## Stop a watch

The stream ends naturally when the container sleeps or shuts down. There are two ways to stop a watch early:

### Use an AbortController

Pass an `AbortSignal` to `parseSSEStream`. Aborting the signal cancels the stream reader, which propagates cleanup to the server. This is the recommended approach when you need to cancel the watch from outside the consuming loop:

* [  JavaScript ](#tab-panel-10784)
* [  TypeScript ](#tab-panel-10785)

JavaScript

```
import { parseSSEStream } from "@cloudflare/sandbox";
const stream = await sandbox.watch("/workspace/src");const controller = new AbortController();
// Cancel after 60 secondssetTimeout(() => controller.abort(), 60_000);
for await (const event of parseSSEStream(stream, controller.signal)) {  if (event.type === "event") {    console.log(`${event.eventType}: ${event.path}`);  }}
console.log("Watch stopped");
```

TypeScript

```
import { parseSSEStream } from "@cloudflare/sandbox";import type { FileWatchSSEEvent } from "@cloudflare/sandbox";
const stream = await sandbox.watch("/workspace/src");const controller = new AbortController();
// Cancel after 60 secondssetTimeout(() => controller.abort(), 60_000);
for await (const event of parseSSEStream<FileWatchSSEEvent>(  stream,  controller.signal,)) {  if (event.type === "event") {    console.log(`${event.eventType}: ${event.path}`);  }}
console.log("Watch stopped");
```

### Break out of the loop

Breaking out of the `for await` loop also cancels the stream:

* [  JavaScript ](#tab-panel-10792)
* [  TypeScript ](#tab-panel-10793)

JavaScript

```
import { parseSSEStream } from "@cloudflare/sandbox";
const stream = await sandbox.watch("/workspace/src");let eventCount = 0;
for await (const event of parseSSEStream(stream)) {  if (event.type === "event") {    console.log(`${event.eventType}: ${event.path}`);    eventCount++;
    // Stop after 100 events    if (eventCount >= 100) {      break; // Breaking out of the loop cancels the stream    }  }}
console.log("Watch stopped");
```

TypeScript

```
import { parseSSEStream } from "@cloudflare/sandbox";import type { FileWatchSSEEvent } from "@cloudflare/sandbox";
const stream = await sandbox.watch("/workspace/src");let eventCount = 0;
for await (const event of parseSSEStream<FileWatchSSEEvent>(stream)) {  if (event.type === "event") {    console.log(`${event.eventType}: ${event.path}`);    eventCount++;
    // Stop after 100 events    if (eventCount >= 100) {      break; // Breaking out of the loop cancels the stream    }  }}
console.log("Watch stopped");
```

## Best practices

### Use server-side filtering

Filter with `include` or `exclude` patterns rather than filtering events in JavaScript. Server-side filtering happens at the inotify level, which reduces the number of events sent over the network.

Note

`include` and `exclude` are mutually exclusive. Use one or the other, not both. If you need to watch specific file types while ignoring certain directories, use `include` patterns that match the files you want.

* [  JavaScript ](#tab-panel-10788)
* [  TypeScript ](#tab-panel-10789)

JavaScript

```
import { parseSSEStream } from "@cloudflare/sandbox";
// Efficient: filtering happens at the inotify levelconst stream = await sandbox.watch("/workspace/src", {  include: ["*.ts"],});
// Less efficient: all events are sent and then filtered in JavaScriptconst stream2 = await sandbox.watch("/workspace/src");for await (const event of parseSSEStream(stream2)) {  if (event.type === "event") {    if (!event.path.endsWith(".ts")) continue;    // Handle event  }}
```

TypeScript

```
import { parseSSEStream } from "@cloudflare/sandbox";import type { FileWatchSSEEvent } from "@cloudflare/sandbox";
// Efficient: filtering happens at the inotify levelconst stream = await sandbox.watch("/workspace/src", {  include: ["*.ts"],});
// Less efficient: all events are sent and then filtered in JavaScriptconst stream2 = await sandbox.watch("/workspace/src");for await (const event of parseSSEStream<FileWatchSSEEvent>(stream2)) {  if (event.type === "event") {    if (!event.path.endsWith(".ts")) continue;    // Handle event  }}
```

### Handle errors in event processing

Errors in your event handler do not stop the watch stream. Wrap handler logic in `try...catch` to prevent unhandled exceptions:

* [  JavaScript ](#tab-panel-10794)
* [  TypeScript ](#tab-panel-10795)

JavaScript

```
import { parseSSEStream } from "@cloudflare/sandbox";
const stream = await sandbox.watch("/workspace/src");
for await (const event of parseSSEStream(stream)) {  if (event.type === "event") {    try {      await handleFileChange(event.eventType, event.path);    } catch (error) {      console.error(        `Failed to handle ${event.eventType} for ${event.path}:`,        error,      );      // Continue processing events    }  }
  if (event.type === "error") {    console.error("Watch error:", event.error);  }}
```

TypeScript

```
import { parseSSEStream } from "@cloudflare/sandbox";import type { FileWatchSSEEvent } from "@cloudflare/sandbox";
const stream = await sandbox.watch("/workspace/src");
for await (const event of parseSSEStream<FileWatchSSEEvent>(stream)) {  if (event.type === "event") {    try {      await handleFileChange(event.eventType, event.path);    } catch (error) {      console.error(        `Failed to handle ${event.eventType} for ${event.path}:`,        error,      );      // Continue processing events    }  }
  if (event.type === "error") {    console.error("Watch error:", event.error);  }}
```

### Ensure directories exist before watching

Watching a non-existent path returns an error. Verify the path exists before starting a watch:

* [  JavaScript ](#tab-panel-10782)
* [  TypeScript ](#tab-panel-10783)

JavaScript

```
const watchPath = "/workspace/src";const result = await sandbox.exists(watchPath);
if (!result.exists) {  await sandbox.mkdir(watchPath, { recursive: true });}
const stream = await sandbox.watch(watchPath, {  include: ["*.ts"],});
```

TypeScript

```
const watchPath = "/workspace/src";const result = await sandbox.exists(watchPath);
if (!result.exists) {  await sandbox.mkdir(watchPath, { recursive: true });}
const stream = await sandbox.watch(watchPath, {  include: ["*.ts"],});
```

## Troubleshooting

### High CPU usage

If watching large directories causes performance issues:

1. Use specific `include` patterns instead of watching everything
2. Exclude large directories like `node_modules` and `dist`
3. Watch specific subdirectories instead of the entire project
4. Use `recursive: false` for shallow monitoring

### Path not found errors

All paths must exist and resolve to within `/workspace`. Relative paths are resolved from `/workspace`.

Container lifecycle

File watchers are automatically stopped when the sandbox sleeps or shuts down. If the sandbox wakes up, you must re-establish watches in your application logic.

## Related resources

* [File Watching API reference](https://developers.cloudflare.com/sandbox/api/file-watching/) — Complete API documentation and types
* [Manage files guide](https://developers.cloudflare.com/sandbox/guides/manage-files/) — File operations
* [Background processes guide](https://developers.cloudflare.com/sandbox/guides/background-processes/) — Long-running processes
* [Stream output guide](https://developers.cloudflare.com/sandbox/guides/streaming-output/) — Real-time output handling

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