npm-watch

Run scripts from package.json when files change.

Common Issues

• monorepo setups: In a monorepo setup, npm-watch may fail with ENOENT. The solution is to have nodemon globally installed. See here for more context

Synopsis

Install it:

npm install npm-watch

Add a top-level "watch" config to your package.json and a "watch" script to your "scripts":

{
  "watch": {
    "test": "{src,test}/*.js"
  },
  "scripts": {
    "test": "tape test/*.js",
    "watch": "npm-watch"
  }
}

There is the possibility to watch for different tasks

  {
    "watch": {
      "run_android": {
        "patterns": [
          "app"
        ],
        "extensions": "ts,html,scss",
        "quiet": false
      },
      "run_ios": {
        "patterns": [
          "app"
        ],
        "extensions": "ts,html,scss",
        "quiet": false
      }
    },
    "scripts": {
      "watch_android": "npm-watch run_android",
      "watch_ios": "npm-watch run_ios",
      "run_android": "tns run android --emulator",
      "run_ios": "tns run ios --emulator"
    }
  }

The top level keys of the "watch" config should match the names of your "scripts", and the values should be a glob pattern or array of glob patterns to watch.

Also it is now possible to obtain a second parameter to define the script which should be run for watching and not watch all possible scripts at once.

If you need to watch files with extensions other than those that nodemon watches by default (.js, .coffee, .litcoffee), you can set the value to an object with patterns and extensions keys. You can also add an ignore key (a list or a string) to ignore specific files. Finally, you can add a quiet flag to hide the script name in any output on stdout or stderr, or you can use the inherit flag to preserve the original's process stdout or stderr. You can enable nodemon legacy watch and specify the restart delay in milliseconds with the corresponding flags.

The quiet flag was changed from a string to a boolean in 0.1.5. Backwards compatibility will be kept for two patch versions.

Use runOnChangeOnly to set the nodemon option --on-change-only. Setting this to true tells nodemon to execute script on change only, not startup.

{
  "watch": {
    "test": {
      "patterns": ["src", "test"],
      "extensions": "js,jsx",
      "ignore": "src/vendor/external.min.js",
      "quiet": true,
      "legacyWatch": true,
      "delay": 2500,
      "runOnChangeOnly": false
    }
  },
  "scripts": {
    "test": "tape test/*.js"
  }
}

Start the watcher with npm run watch in a terminal, then edit some files:

mkdir src test
npm run watch &
cat <<EOF > test/test-sum.js
var test = require('tape')
test('sum module', function (t) {
  var sum = require('../src/sum.js')
  t.ok(sum(1, 2), 3, "Sums appear correct")
  t.end()
})
EOF

(Feel free to use the editor of your choice, cat just makes for easy demos)

You should see that your tests ran automatically, and failed because src/sum.js is missing. Let's fix that:

cat <<EOF > src/sum.js
module.exports = function (a, b)  {
  return 1
}
EOF

Our tests will run again, and this time they almost work. Let's fix sum.js:

cat <<EOF > src/sum.js
module.exports = function (a, b)  {
  return a + b
}
EOF

Tests run perfectly, ship it to the enterprise!

Once you have the watcher running, you can force restart all tasks by entering rs. If you want to only force a single task, type the name of the key from the watch config (for example rs test).

Global Config

setMaxListeners

If too many listeners are added to an event emitter, node.js will send a warning (rightfully so) about potential memory leaks. The default maximum is 10. If you need more than that, you can add a top level global config to your package.json

"watchGlobalConfig": {
    "setMaxListeners": true
}

And max listeners will be set on the relevant processes to the minimum needed to avoid the warning.

Options

patterns

Array of paths to watch

"patterns": ["src", "test"]

extensions

Comma delimited list of file extensions to watch

"extensions": "js,jsx"

ignore

Add an ignore property to your watch object. The value of ignore can be a string if you only want to ignore a single glob:

"watch": {
  "build": {
    "ignore": "build",
    ...
  }
  ...
}

Or an array if you want to ignore multiple globs:

"watch": {
  "build": {
    "ignore": [
      "build",
      "node_modules"
    ],
    ...
  }
  ...
}

quiet

Boolean to hide the script name in any output on stdout and stderr

"quiet": false

inherit

Boolean to preserve the original process' stdout and stderr

"inherit": false

legacyWatch

Boolean to enable legacy watch

"legacyWatch": true

delay

Number of milliseconds to delay before checking for new files

"delay": 2500

clearBuffer

Boolean to clear the buffer after detecting a new change

"clearBuffer": true

verbose

Boolean to turn on the nodemons verbose mode

"verbose": true

silent

Boolean to turn on nodemons silent (quiet) mode Silent was used as we already had an existing flag called quiet. This may change in a future release

"silent": true

Acknowledgements

This module does very little but run nodemon for you, all credit for the reliable file watching and process restarting should go to there.

License

MIT