Nearsighted Paramecium Multiverse

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    1.0.7-e • Public • Published

    npm version

    This async TS/JS code is to programmatically execute/fork external/shell commands and npm/yarn scripts from Node. The major assumed case is smart repo maintenance, running npm/yarn/pnpm scripts, when your Node app/script launches a script from package.json like yarn deploy:moduleX -- hence the npm-spawner package name. Also it provides a general mean (spawnNodeChild) to execute anything the async (standard version) spawn method of the Node's child_process can. In a callback/event handler/hook fashion it exposes the events, the ChildProcess event emitter itself and returns a promise to the final status of the execution (a less detailed one than the spawnSync version would).

    In Node spawn is the variant of exec that one would use for external processes emitting stuff to stdio. This by default does not create a shell so is less vulnerable.


    The reason is to circumvent "The programmatic API was removed in npm v8.0.0" problem. The other motivation was to find a workaround with the current state of the 'concurrently' module when recursive use of it resulted in loss of stdout.

    Usage examples

    errors.build6 = false;
    greeting = "Repo manager: building module #6";
    await npmSpawner( "run build:module-6", {
        npm: "yarn",    // may you prefer yarn over npm
        onProblem: (err,event) => { // 'problem', since it's not necesseraly an error
            errors.build6 = true;
            console.warn(greeting,"failed on",event,"and says:",err.message);
        onClose: code => console.log(greeting,"closed with:",code),
    if (!errors.build6) {
        await npmSpawner( "run depoloy");

    You also get a more general "spawner", spawnNodeChild for launching any system command or binary:

    const {code:testResult} = await spawnNodeChild(
        "test", // the command-line unix utility
        "-f $FILENAME42",   // the args, which can now be in space-separated normal form
            cwd: process.cwd(), // redundant, just illustrating the separate cwd option
            suppressShellWarning: true,
            nodeSpawnOptions: {
                shell: true,  // executing shell commands require a child shell many times
                env: {
                    FILENAME42: "package.json"
    console.log("Package.json:",testResult===0? "exists.":"is missing or we otherwise failed to test it.");
    // the sane solution should have been simply to call fs.existsSync(projectPackageJsonPath) :))


    • spawnNodeChild (and the npmSpawner which just wraps the former) are using the normal async version of child_process.spawn, or rather convert the 'spawn():<ChildProcess> + event hooks' model to the async form, so it's more intuitive to use while the benefits of lifecycle events are still available via the ChildProcess event hooks.
    • When not awaiting, the execution will take the async/concurrent flow. And the ChildProcess event emitter is available from the getSpawnedProc callback (the emitter otherwise returned by the child_process.spawn).
    • Unlike with pure spawn you can provide args as a space-separated single string.
    • The resolved returned shape holds the 'exit' code (returned by the close event), the signal if terminated and the error/problem code if previously exit or error events dropped one.
    • Note: this package primarily delivers a pure ESM module.
    • When ran within a ts-node scenario:
      • May need to import npm-spawner/index.js (try importing from npm-spawner first).
      • node --loader ts-node/esm ./your-app.ts
    • The alternative CommonJS usage:
      • Import or require from the npm-spawner/cjs/index.js bundle.
      • This bundling supposedly prevents the 'dual package hazard'.
    • By default stdin,stdout and stderr are inherited from the calling Node process.
    • shell is by default set to false, and if enabled one needs to set an additional flag to mute a warning reminding us about the vulnerable nature of this choice.


    async function spawnNodeChild (
      command: string,
      args: string|string[],  // args as an array of strings as per the spawn signature, or a string with space separated args
      options?: SpawnNodeChildOptions
    ): Promise<SpawnNodeChildReturnT> {}
    async function npmSpawner (
      args: string|string[],  // args as an array of strings as per the spawn signature, or a string with space separated args
      options?: NpmSpawnerOptions
    ): Promise<SpawnNodeChildReturnT> {}
    type SpawnNodeChildReturnT = {
      code: number|null,
      problemCollected?: Error,
      signal?: NodeJS.Signals|null
    type SpawnNodeChildOptions = {
      cwd?: string,  // extracted for convenience, injected to nodeSpawnOptions.cwd
      nodeSpawnOptions?: SpawnOptionsWithoutStdio,  // the standard child_process.spawnSync options
      onClose?: (
        code: SpawnNodeChildReturnT['code'],
        problemCollected?: SpawnNodeChildReturnT['problemCollected'],
        signal?: SpawnNodeChildReturnT['signal']
      ) =>void,
      // the hook on the 'close' event which will fire anyway after error/exit/problem (except the exception probably), 
      // use to finalize the run and mind not to double handle events
      // expect onProblem be emitted prior to onClose
      onProblem?: (err: Error, event: 'error'|'exit') =>void,
      // the hook on the 'error' event, and also when 'exit' returns a non-zero exit code 
      // also overtakes onNodeError, but not onClose and not the thrown exceptions
      onNodeError?: (err: Error, event: 'error'|'_exception') =>void,
      // ChildProcess/'error' event which belongs to execution and not to the error events with the command
      // not reachable if onProblem is specified
      // try/catch exceptions are also sent here
      noStdioInheritance?: boolean,
      // 'inherit' is the forced setting for stdio (bound to process.std*), this resets the behaviour to undefined
      suppressShellWarning?: boolean,  // mind not to make it vulnerable
      getSpawnedProc?: (childProc: ChildProcess) =>void
    type NpmSpawnerOptions = SpawnNodeChildOptions & {
        npm?: string, // lets you specify 'yarn'

    "If the shell option is enabled, do not pass unsanitized user input to this function. Any input containing shell metacharacters may be used to trigger arbitrary command execution."

    Consult also:


    • This module uses no dependencies except Node itself. The small code is simple to review.
    • The functionality it opens up may have serious security implications so implement carefully and submit for code review by a competent person (eg. security engineer/champion or pentester).
    • If the use case remains within the frame of local CLI then exposing utilities/scripts via this code will not extend the existing risks (as compared to the user launching codes via npm/node directly).
    • If this code bridges access to machine hosted scripts (running with local user privileges) from a webinterface available remotely then containment (jailing), strict user authentication, access controls and continuous security code-review is necessary.


    • For the ESM, TS-Node and CommonJs issues see the Explainer section above.
    • May esbuild drop a warning Top-level "this" will be replaced with undefined since this file is an ECMAScript module try using --define:this=globalThis option like esbuild ./src/app.ts --bundle --outfile=./bin/app.js --platform=node --format=esm --define:this=globalThis.

    Useful stuff

    • import * as path from 'node:path'
    • import * as fs from 'graceful-fs'
    • import chalk from 'chalk'
    • import {concurrently} from 'concurrently'
    • import * as oclif from '@oclif/core'


    • issue submission
    • twitter: timurxyz


    npm i npm-spawner

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