Extremely fast file change detector and task orchestrator for Node.js.
If you ever wanted something like Nodemon but more capable, then you are at the right place.
Basic usage:
npm install turbowatch
cat > turbowatch.ts <<'EOD'
import { defineConfig } from 'turbowatch';
export default defineConfig({
project: __dirname,
triggers: [
{
expression: ['match', '*.ts', 'basename'],
name: 'build',
onChange: async ({ spawn }) => {
await spawn`tsc`;
},
},
],
});
EOD
npm exec turbowatch ./turbowatch.tsNote See logging instructions to print logs that explain what Turbowatch is doing.
Refer to recipes:
- Rebuilding assets when file changes are detected
- Restarting server when file changes are detected
- Retrying failing triggers
- Gracefully terminating Turbowatch
- Handling the
AbortSignal - Tearing down project
- Throttling
spawnoutput - Watching multiple scripts
- Using custom file watching backend
| Turbowatch | Nodemon | |
|---|---|---|
| Node.js interface (scriptable) | ✅ | ❌1 |
| Graceful termination (teardown) | ✅ | ❌2 |
| Scriptable child processes (zx) | ✅ | ❌ |
| Retries | ✅ | ❌ |
| Debounce | ✅ | ❌ |
| Interruptible workflows | ✅ | ❌ |
| Concurrent workflows | ✅ | ❌ |
| Log grouping | ✅ | ❌ |
| Bring-your-own backend | ✅ | ❌ |
| Works with long-running processes | âś… | âś… |
| Works with build utilities and REPLs | âś… | âś… |
| Watch specific files or directories | âś… | âś… |
| Ignoring specific files or directories | âś… | âś… |
| Open source and available | âś… | âś… |
1 Undocumented
2 Nodemon only provides the ability to send a custom signal to the worker.
Note
defineConfigis used to export configuration for the consumption byturbowatchprogram. If you want to run Turbowatch programmatically, then usewatch. The API of both methods is equivalent.
Turbowatch defaults are a good choice for most projects. However, Turbowatch has many options that you should be familiar with for advance use cases.
import {
watch,
type ChangeEvent,
} from 'turbowatch';
void watch({
// Debounces triggers by 1 second.
// Most multi-file spanning changes are non-atomic. Therefore, it is typically desirable to
// batch together information about multiple file changes that happened in short succession.
// Provide { debounce: { wait: 0 } } to disable debounce.
debounce: {
wait: 1000,
},
// The base directory under which all files are matched.
// Note: This is different from the "root project" (https://github.com/gajus/turbowatch#project-root).
project: __dirname,
triggers: [
{
// Expression match files based on name.
// https://github.com/gajus/turbowatch#expressions
expression: [
'allof',
['not', ['dirname', 'node_modules']],
[
'anyof',
['match', '*.ts', 'basename'],
['match', '*.tsx', 'basename'],
]
],
// Indicates whether the onChange routine should be triggered on script startup.
// Defaults to true. Set it to false if you would like onChange routine to not run until the first changes are detected.
initialRun: true,
// Determines what to do if a new file change is detected while the trigger is executing.
// If {interruptible: true}, then AbortSignal will abort the current onChange routine.
// If {interruptible: false}, then Turbowatch will wait until the onChange routine completes.
// Defaults to true.
interruptible: false,
// Name of the trigger. Used for debugging
// Must match /^[a-z0-9-_]+$/ pattern and must be unique.
name: 'build',
// Routine that is executed when file changes are detected.
onChange: async ({ spawn }: ChangeEvent) => {
await spawn`tsc`;
await spawn`tsc-alias`;
},
// Routine that is executed when shutdown signal is received.
onTeardown: async ({ spawn }) => {
await spawn`rm -fr ./dist`;
},
// Label a task as persistent if it is a long-running process, such as a dev server or --watch mode.
persistent: false,
// Retry a task if it fails. Otherwise, watch program will throw an error if trigger fails.
// Defaults to { retries: 3 }
retry: {
retries: 3,
},
},
],
});To abstract the complexity of orchestrating file watching operations.
For context, we are using Turborepo. The reason this project came to be is because Turborepo does not have "watch" mode (issue #986).
At first, we attempted to use a combination of tsc --watch, concurrently and Nodemon, but started to run into things breaking left and right, e.g.
- services restarting prematurely (before all the assets are built)
- services failing to gracefully shutdown and then failing to start, e.g. because ports are in use
Furthermore, the setup for each workspace was repetitive and not straightforward, and debugging issues was not a great experience because you have many workspaces running in watch mode producing tons of logs. Many of the workspaces being dependencies of each other, this kept re-triggering watch operations causing the mentioned issues.
In short, it quickly became clear that we need the ability to have more control over the orchestration of what/when needs to happen when files change.
We started with a script. At first I added debounce. That improved things. Then I added graceful termination logic, which mostly made everything work. We still had occasional failures due to out-of-order events, but adding retry logic fixed that too... At the end, while we got everything to work, it took a lot of effort and it still was a collection of hacky scripts that are hard to maintain and debug, and that's how Turbowatch came to be –
Turbowatch is a toolbox for orchestrating and debugging file watching operations based on everything we learned along the way.
Note If you are working on a very simple project, i.e. just one build step or just one watch operation, then you don't need Turbowatch. Turbowatch is designed for monorepos or otherwise complex workspaces where you have dozens or hundreds of build steps that depend on each other (e.g. building and re-building dependencies, building/starting/stopping Docker containers, populating data, sending notifications, etc).
We also shared these learnings with Turborepo team in hopes that it will help to design an embedded file watching experience.
Turbowatch can be used to automate any sort of operations that need to happen in response to files changing, e.g.,
- You can run (and conditionally restart) long-running processes (like your Node.js application)
- You can build assets (like TypeScript and Docker images)
Turbowatch exposes spawn function that is an instance of zx. Use it to evaluate shell commands:
async ({ spawn }: ChangeEvent) => {
await spawn`tsc`;
await spawn`tsc-alias`;
},The reason Turbowatch abstracts zx is to enable graceful termination of child-processes when triggers are configured to be interruptible.
Your setup may include tasks that are not designed to exit, e.g. next dev (starts Next.js in development mode).
It is important that these tasks are marked as persistent to distinguish them from tasks that run to completion as that changes how Turbowatch treats them.
| Persistent | Non-Persistent | |
|---|---|---|
Ignore FileChangeEvent if { interruptible: false } |
✅ | ❌ |
Expressions are used to match files. The most basic expression is match – it evaluates as true if a glob pattern matches the file, e.g.
Match all files with *.ts extension:
['match', '*.ts', 'basename']Expressions can be combined using allof and anyof, e.g.,
Match all files with *.ts or *.tsx extensions:
[
'anyof',
['match', '*.ts', 'basename'],
['match', '*.tsx', 'basename']
]Finally, not evaluates as true if the sub-expression evaluated as false, i.e. inverts the sub-expression.
Match all files with *.ts extension, but exclude index.ts:
[
'allof',
['match', '*.ts', 'basename'],
[
'not',
['match', 'index.ts', 'basename']
]
]This is the gist behind Turbowatch expressions. However, there are many more expressions. Inspect Expression type for further guidance.
type Expression =
// Evaluates as true if all of the grouped expressions also evaluated as true.
| ['allof', ...Expression[]]
// Evaluates as true if any of the grouped expressions also evaluated as true.
| ['anyof', ...Expression[]]
// Evaluates as true if a given file has a matching parent directory.
| ['dirname' | 'idirname', string]
// Evaluates as true if a glob matches against the basename of the file.
| ['match' | 'imatch', string, 'basename' | 'wholename']
// Evaluates as true if the sub-expression evaluated as false, i.e. inverts the sub-expression.
| ['not', Expression];Note Turbowatch expressions are a subset of Watchman expressions. Originally, Turbowatch was developed to leverage Watchman as a superior backend for watching a large number of files. However, along the way, we discovered that Watchman does not support symbolic links (issue #105). Unfortunately, that makes Watchman unsuitable for projects that utilize linked dependencies (which is the direction in which the ecosystem is moving for dependency management in monorepos). As such, Watchman was replaced with chokidar. We are hoping to provide Watchman as a backend in the future. Therefore, we made Turbowatch expressions syntax compatible with a subset of Watchman expressions.
Note Turbowatch uses micromatch for glob matching. Please note that you should be using forward slash (
/) to separate paths, even on Windows.
import { watch } from 'turbowatch';
void watch({
project: __dirname,
triggers: [
{
expression: [
'allof',
['not', ['dirname', 'node_modules']],
['match', '*.ts', 'basename'],
],
name: 'build',
onChange: async ({ spawn }) => {
await spawn`tsc`;
await spawn`tsc-alias`;
},
},
],
});import { watch } from 'turbowatch';
void watch({
project: __dirname,
triggers: [
{
expression: [
'allof',
['not', ['dirname', 'node_modules']],
[
'anyof',
['match', '*.ts', 'basename'],
['match', '*.graphql', 'basename'],
]
],
// Because of this setting, Turbowatch will kill the processes that spawn starts
// when it detects changes when it detects a change.
interruptible: true,
name: 'start-server',
onChange: async ({ spawn }) => {
await spawn`tsx ./src/bin/wait.ts`;
await spawn`tsx ./src/bin/server.ts`;
},
},
],
});There is more than one way to watch node_modules. However, through trial and error we found that the following set of rules work the best for a generalized solution.
import { watch } from 'turbowatch';
void watch({
project: path.resolve(__dirname, '../..'),
triggers: [
{
expression: [
'anyof',
[
'allof',
['dirname', 'node_modules'],
['dirname', 'dist'],
['match', '*', 'basename'],
],
[
'allof',
['not', ['dirname', 'node_modules']],
['dirname', 'src'],
['match', '*', 'basename'],
],
],
name: 'build',
onChange: async ({ spawn }) => {
return spawn`pnpm run build`;
},
},
],
});This setup makes an assumption that your workspaces sources are in src directory and build task outputs to dist directory.
This might be common sense, but since Turbowatch scripts are regular JavaScript scripts, you can (and should) abstract your expressions and routines.
How you do it is entirely up to you, e.g. You could abstract just expressions or you could go as far as abstracting the entire trigger:
import { watch } from 'turbowatch';
import {
buildTrigger,
} from '@/turbowatch';
void watch({
project: __dirname,
triggers: [
buildTrigger(),
],
});Such abstraction helps to avoid errors that otherwise may occur due to duplicative code across workspaces.
Something that is important to consider when orchestrating file watching triggers is how to avoid unnecessary reloads. Consider if this was your "build" script:
rm -fr dist && tsc && tsc-aliasand let's assume that you are using an expression such as this one to detect when dependencies are updated:
[
'allof',
['dirname', 'node_modules'],
['dirname', 'dist'],
['match', '*'],
],Running this script will produce at least 3 file change events:
- when
rm -fr distcompletes - when
tsccompletes - when
tsc-aliascompletes
What's even worse is that even if the output has not changed, you are still going to trigger file change events (because dist get replaced).
To some degree, debounce setting helps with this. However, it will only help if there is no more than 1 second (by default) inbetween every command.
One way to avoid this entirely is by using an intermediate directory to output files and swapping only the files that changed. Here is how we do it:
rm -fr .dist && tsc --project tsconfig.build.json && rsync -cr --delete .dist/ ./dist/ && rm -fr .distThis "build" script will always produce at most 1 event, and won't produce any events if the outputs have not changed.
This is not specific to Turbowatch, but something worth considering as you are designing your build pipeline.
Retries are configured by passing a retry property to the trigger configuration.
/**
* @property factor The exponential factor to use. Default is 2.
* @property maxTimeout The maximum number of milliseconds between two retries. Default is 30,000.
* @property minTimeout The number of milliseconds before starting the first retry. Default is 1000.
* @property retries The maximum amount of times to retry the operation. Default is 3. Seting this to 1 means do it once, then retry it once.
*/
type Retry = {
factor?: number,
maxTimeout?: number,
minTimeout?: number,
retries?: number,
}Note
SIGINTis automatically handled if you are usingturbowatchexecutable to evaluate your Turbowatch script. This examples shows how to programmatically gracefully shutdown Turbowatch if you choose not to useturbowatchprogram to evaluate your watch scripts.
Warning Unfortunately, many tools do not allow processes to gracefully terminate. There are open support issues for this in npm (#4603), pnpm (#2653) and yarn (#4667), but they haven't been addressed. Therefore, do not wrap your
turbowatchscript execution using these tools if you require processes to gracefully terminate.
watch returns an instance of TurbowatchController, which can be used to gracefully terminate the script:
const { shutdown } = await watch({
project: __dirname,
triggers: [
{
name: 'test',
expression: ['match', '*', 'basename'],
onChange: async ({ spawn }) => {
// `sleep 60` will receive `SIGTERM` as soon as `shutdown()` is called.
await spawn`sleep 60`;
},
}
],
});
// SIGINT is the signal sent when we press Ctrl+C
process.once('SIGINT', () => {
void shutdown();
});Invoking shutdown will propagate an abort signal to all onChange handlers. The processes that were initiated using spawn will receive SIGTERM signal.
In addition to being to Turbowatch using the shutdown routine, Turbowatch instance can be shutdown using an AbortController. The main difference is that shutdown can be awaited to know when the shutdown routine has run to completion.
const abortController = new AbortController();
void watch({
abortController,
project: __dirname,
triggers: [
{
name: 'test',
expression: ['match', '*', 'basename'],
onChange: async ({ spawn }) => {
// `sleep 60` will receive `SIGTERM` as soon as `shutdown()` is called.
await spawn`sleep 60`;
},
}
],
});
void abortController.abort();Workflow might be interrupted in two scenarios:
- when Turbowatch is being gracefully shutdown
- when routine is marked as
interruptibleand a new file change is detected
Implementing interruptible workflows requires that you define AbortSignal handler. If you are using zx, such abstraction could look like so:
Note Turbowatch already comes with
zxbound to theAbortSignal. Just usespawn. Documentation demonstrates how to implement equivalent functionality.
import { type ProcessPromise } from 'zx';
const interrupt = async (
processPromise: ProcessPromise,
abortSignal: AbortSignal,
) => {
let aborted = false;
const kill = () => {
aborted = true;
processPromise.kill();
};
abortSignal.addEventListener('abort', kill, { once: true });
try {
await processPromise;
} catch (error) {
if (!aborted) {
console.log(error);
}
}
abortSignal.removeEventListener('abort', kill);
};which you can then use to kill your scripts, e.g.
export default watch({
project: __dirname,
triggers: [
{
expression: ['match', '*.ts', 'basename'],
interruptible: false,
name: 'sleep',
onChange: async ({ abortSignal }) => {
await interrupt($`sleep 30`, abortSignal);
},
},
],
});