Watching for File Changes

Contents

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

npm i 
npm i -g

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

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

npm i -g 
npm link

Define Run Command

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

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

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

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

const app = require('commander')

const split = val => val.split(',')

app.version('0.1.0')
    .option('-d, --dirs [directories]', 'List of directories to watch', split)
    .option(
        '-c, --commands [directory]',
        'List of Commands to run when files change',
        split
    )
    .option(
        '-f, --exclude-files [files to exclude]',
        'List of Files to Exclude from Watch',
        split
    )
    .option(
        '-e, --exclude-extensions [extensions to exclude]',
        'List of Extensions to Exclude from Watch',
        split
    )
    .option(
        '-D, --exclude-directories [directories to exclude]',
        'List of Directories to Exclude from Watch',
        split
    )
    .parse(process.argv)

console.log('Called with the following Options')

if (app.dirs) console.log('dirs:', app.dirs)
if (app.commands) console.log('commands:', app.commands)
if (app.excludeFiles) console.log('excluded files:', app.excludeFiles)
if (app.excludeExtensions)
    console.log('excluded extensions:', app.excludeExtensions)
if (app.excludeDirectories)
    console.log('excluded directories:', app.excludeDirectories)

We can also get help and information on the commands with

startover -h

Watcher Events

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

// Initialize watcher.
var watcher = chokidar.watch('.', {
    ignored: new Array().concat(
        app.excludeDirectories,
        app.excludeFiles,
        new RegExp(app.excludeExtensions.map(el => '.' + el).join('|'))
    ),
    persistent: true
})

// Something to use when events are received.
var log = console.log.bind(console)

// Add event listeners.
var ready = false;

watcher
    .on('add', path => console.log(`File ${path} has been added`))
    .on('change', path => {
        if (ready) execute()
        log(`File ${path} has been changed`)
    })
    .on('unlink', path => {
        if (ready) execute()
        log(`File ${path} has been removed`)
    })
    .on('addDir', path => {
        if (ready) execute()
        log(`Directory ${path} has been added`)
    })
    .on('unlinkDir', path => {
        if (ready) execute()
        log(`Directory ${path} has been removed`)
    })
    .on('error', error => log(`Watcher error: ${error}`))
    .on('ready', () => {
        ready = true;
        log('Initial scan complete. Ready for changes')
    })

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

const child_process = require('child_process')

// Utility functions
const split = val => val.split(',')

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

Run Startover

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

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