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    3.2.0 • Public • Published


    Build Status SemVer License

    Offload your heavy lifting to a daemon. Extracted from eslint_d.


    This will install the core_d as a dependency:

    ❯ npm install core_d


    You need to create a main file that controls the daemon and a service.js file which will run in the background.

    The main file should look something like this:

    const cmd = process.argv[2];
    process.env.CORE_D_TITLE = 'your_d';
    process.env.CORE_D_DOTFILE = '.your_d';
    process.env.CORE_D_SERVICE = require.resolve('./your-service');
    const core_d = require('core_d');
    if (cmd === 'start'
      || cmd === 'stop'
      || cmd === 'restart'
      || cmd === 'status') {

    The service.js file must expose an invoke function like this:

     * The core_d service entry point.
    exports.invoke = function (cwd, args, text, mtime) {
      return 'Your response';

    How does this work?

    The first time you call core_d.invoke(...), a little server is started in the background and bound to a random port. The port number is stored along with a security token in the configured dotfile. Your services invoke method is called with the same arguments. Later calls to invoke will be executed on the same instance. So if you have a large app that takes a long time to load, but otherwise responds quickly, and you're using it frequently, like linting a file, then core_d can give your tool a performance boost.


    The core_d client exposes these functions:

    • start(): Starts the background server and create the dotfile. It's not necessary to call this since invoke will start the server if it's not already running.
    • stop(): Stops the background server and removed the dotfile.
    • restart(): Stops and starts the background server again.
    • status(): Prints a status message saying whether the server is running or not. If the server is running and your service implements getStatus(), the return value will be printed as well.
    • invoke(cwd, args[, text]): Invokes the invoke methods in the service.

    Environment variables:

    • CORE_D_TITLE: The process title to use. Optional.
    • CORE_D_DOTFILE: The name of dotfile to use, e.g. .core_d.
    • CORE_D_SERVICE: The resolved path to the service implementation. Use require.resolve('./relative-path') to receive the resolved path.

    Your service must implement a function with the signature invoke(cwd, args, text, mtime, callback). The passed arguments are:

    • cwd: The current working directory.
    • args: The first argument passed to core_d.invoke.
    • text: The second argument passed to core_d.invoke.
    • mtime: The newest mtime returns from fs.stat on any of these files:
      • package.json
      • package-lock.json
      • npm-shrinkwrap.json
      • yarn.lock
      • pnpm-lock.yaml Use this to flush any caches if mtime is newer than the last value received.
    • callback: A callback function with the signature (err, response).

    The service can optionally implement a getStatus() function to return additional status information when calling core_d.status().

    Moar speed

    If you're really into performance and want the lowest possible latency, talk to the core_d server with netcat. This will also eliminate the node.js startup time on the client side.

    ❯ PORT=`cat ~/.core_d | cut -d" " -f1`
    ❯ TOKEN=`cat ~/.core_d | cut -d" " -f2`echo "$TOKEN $PWD file.js" | nc localhost $PORT

    Or if you want to work with stdin:

    echo "$TOKEN $PWD --stdin" | cat - file.js | nc localhost $PORT


    • 3.0.0: node 10, 12 and 14
    • 2.0.0: node 10, 12 and 14
    • 1.0.0: node 6, 8 and 10




    npm i core_d

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