npm-watch

What is npm-watch?

npm-watch is a utility that allows you to run scripts in response to file changes. It is particularly useful for automating tasks such as building, testing, or linting your code whenever you make changes.

What are npm-watch's main functionalities?

Watch and Run Scripts

This feature allows you to watch specific files or directories and run a script when changes are detected. In this example, the 'build' script will run whenever a JavaScript file in the 'src' directory changes.

{
  "scripts": {
    "build": "webpack",
    "watch": "npm-watch"
  },
  "watch": {
    "build": {
      "patterns": ["src/**/*.js"],
      "extensions": "js"
    }
  }
}

Custom Watch Patterns

You can specify custom patterns to watch multiple directories or file types. In this example, the 'test' script will run whenever a JavaScript file in either the 'test' or 'src' directories changes.

{
  "scripts": {
    "test": "mocha",
    "watch": "npm-watch"
  },
  "watch": {
    "test": {
      "patterns": ["test/**/*.js", "src/**/*.js"],
      "extensions": "js"
    }
  }
}

Run Multiple Scripts

You can configure npm-watch to run multiple scripts based on different file changes. In this example, both 'lint' and 'build' scripts are set to run when JavaScript files in the 'src' directory change.

{
  "scripts": {
    "lint": "eslint .",
    "build": "webpack",
    "watch": "npm-watch"
  },
  "watch": {
    "lint": {
      "patterns": ["src/**/*.js"],
      "extensions": "js"
    },
    "build": {
      "patterns": ["src/**/*.js"],
      "extensions": "js"
    }
  }
}

Other packages similar to npm-watch

nodemon

Nodemon is a utility that monitors for any changes in your source and automatically restarts your server. It is more focused on server-side applications and is widely used for Node.js development. Unlike npm-watch, which can run any npm script, nodemon is primarily used for restarting Node.js applications.

chokidar

Chokidar is a highly efficient file watcher that can be used to watch file changes and trigger custom actions. It provides a more low-level API compared to npm-watch, allowing for more granular control over file watching and event handling.

watch

The 'watch' package is a simple utility for watching changes in files or directories and executing commands. It is similar to npm-watch but offers fewer configuration options and is more lightweight.

README

npm-watch

Run scripts from package.json when files change.

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"
  }
}

Possibilty 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 compatability 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!

Options

patterns

Array of paths to watch

extensions

Array of file extensions to watch

ignore

String or array of paths to ignore

quiet

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

inherit

Boolean to preserve the original process' stdout and stderr

legacyWatch

Boolean to enable legacy watch

delay

Number of milliseconds to delay before checking for new files

clearBuffer

Boolean to clear the buffer after detecting a new change

verbose

Boolean to turn on the nodemons verbose mode

Ignore files

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"
    ],
    ...
  }
  ...
}

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