Spawn a process to inspect it.
Last updated 2 years ago by thlorenz .
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Spawn a process to inspect it.


npm install ispawn



Configures a process to be spawned but doesn't spawn it yet


  • $0 Objects options (same as @see spawn)

Returns Spawner that will spawn the configured process via spawner.spawn


Spawns a process with the given options allowing to intercept stdout and stderr output of the application itself or the underlying process, i.e. V8 and Node.js messages.

onStdout and onStderr interceptors

The functions, onStdout, onStderr called with each line written to the respective file descriptor have the following signature:

onStdout(line:String, fromApp:Boolean) where fromApp is true when the line came from the app itself and false when it came from the underlying runtime, i.e. Node.js or V8 when flags triggered diagnostics output.

To mark a line as handled return true from the function and it will not be printed to the console.


 function onStdout(line, fromApp) {
   // Don't intercept app output, just have it printed as usual
   if (fromApp) return false
   // Do something with diagnositics messages here ...

   return true
 const { termination } = spawn({
     execArgv: [ '--trace-turbo-inlining' ]
   , argv: [ require.resolve('./bind.js') ]
   , onStdout

 try {
   const code = await termination
   console.log('The app returned with code', code)
 } catch (err) {

full example


  • $0 Object options
    • $0.execArgv Array<String>? arguments passed to Node.js/V8 directly (not to your app) (optional, default [])
    • $0.argv Array<String> file to run followed by flags to pass to your app
    • $0.node String? path to Node.js executable (optional, default process.execPath)
    • $0.spawnOpts Object? options passed to child_process.spawn (optional, default {})
    • $0.onStdout Function? function to call with each line written to stdout (optional, default null)
    • $0.onStderr Function? function to call with each line written to stderr (optional, default null)

Returns Object with the following properties- termination: {Promise} that resolves when process exits

  • proc: the spawned process


Lots of the ideas and code were extracted from the 0x tool.



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