Watching for File Changes

Updated: 03 September 2023

Essentially I’m trying to do something like nodemon and forever but just a lot simpler and that will suit my needs better

Running Dev

Clone the GitHub Repo, and then install the app dependencies and install the application globally

Terminal window
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npm i
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npm i -g

Next we can link NPM to our actual package instead of the global version with

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npm link

What’s Happening Here

Getting Started

We have a simple node app that is running globally, but linked to our application’s index.js file with the following

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npm i -g
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npm link

Define Run Command

Next we the startover command linked in our package.json as follows

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{
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  "name": "startover",
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  "version": "0.0.0",
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  "description": "Rerun scripts on file change",
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  "main": "index.js",
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  "scripts": { ... },
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  "bin": {
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    "startover": "./index.js"
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  },
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  ...
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}

This will allow us to run th index.js file which is done by simply running the following command

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startover

Parsing Command Line Arguments

We make use of the commander package to parse CLI arguments, we do this from the index.js file and parses the various parameters

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const app = require('commander')
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const split = (val) => val.split(',')
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app
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  .version('0.1.0')
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  .option('-d, --dirs [directories]', 'List of directories to watch', split)
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  .option(
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    '-c, --commands [directory]',
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    'List of Commands to run when files change',
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    split
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  )
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  .option(
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    '-f, --exclude-files [files to exclude]',
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    'List of Files to Exclude from Watch',
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    split
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  )
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  .option(
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    '-e, --exclude-extensions [extensions to exclude]',
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    'List of Extensions to Exclude from Watch',
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    split
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  )
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  .option(
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    '-D, --exclude-directories [directories to exclude]',
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    'List of Directories to Exclude from Watch',
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    split
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  )
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  .parse(process.argv)
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console.log('Called with the following Options')
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if (app.dirs) console.log('dirs:', app.dirs)
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if (app.commands) console.log('commands:', app.commands)
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if (app.excludeFiles) console.log('excluded files:', app.excludeFiles)
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if (app.excludeExtensions)
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  console.log('excluded extensions:', app.excludeExtensions)
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if (app.excludeDirectories)
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  console.log('excluded directories:', app.excludeDirectories)

We can also get help and information on the commands with

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startover -h

Watcher Events

I then defined the events for the file watcher as well as the configuration

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// Initialize watcher.
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var watcher = chokidar.watch('.', {
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  ignored: new Array().concat(
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    app.excludeDirectories,
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    app.excludeFiles,
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    new RegExp(app.excludeExtensions.map((el) => '.' + el).join('|'))
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  ),
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  persistent: true,
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})
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// Something to use when events are received.
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var log = console.log.bind(console)
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// Add event listeners.
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var ready = false
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watcher
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  .on('add', (path) => console.log(`File ${path} has been added`))
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  .on('change', (path) => {
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    if (ready) execute()
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    log(`File ${path} has been changed`)
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  })
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  .on('unlink', (path) => {
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    if (ready) execute()
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    log(`File ${path} has been removed`)
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  })
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  .on('addDir', (path) => {
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    if (ready) execute()
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    log(`Directory ${path} has been added`)
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  })
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  .on('unlinkDir', (path) => {
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    if (ready) execute()
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    log(`Directory ${path} has been removed`)
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  })
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  .on('error', (error) => log(`Watcher error: ${error}`))
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  .on('ready', () => {
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    ready = true
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    log('Initial scan complete. Ready for changes')
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  })

And finally added a function to carry out the custom command that I need to be run

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const child_process = require('child_process')
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// Utility functions
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const split = (val) => val.split(',')
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const execute = () => {
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  app.commands.forEach((command) => {
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    child_process.exec(command, function (error, stdout, stderr) {
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      if (stdout) console.log('command out:\n ' + stdout)
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      if (stderr) console.log('stderr:\n' + stderr)
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      if (error !== null) console.log('exec error: ' + error)
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    })
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  })
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}

Run Startover

We can run startover once it is installed with the following command

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startover -d myapp -f hello.js,"bye world.html" -e css,md -c "npm run build" -D test,

It is important to remember that the command/commands we are running from the -c option must be compatible with the system/shell we are running startover in and they will run one after the other

Resources

I’ve made use of a few different resources for the application as follows

Articles

Libraries