@expo/spawn-async
v1.7.2
Published
A Promise-based interface into processes created by child_process.spawn
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spawn-async
A cross-platform version of Node's child_process.spawn
as an async function that returns a promise. Supports Node 12 LTS and up.
Usage:
import spawnAsync from '@expo/spawn-async';
(async function () {
let resultPromise = spawnAsync('echo', ['hello', 'world']);
let spawnedChildProcess = resultPromise.child;
try {
let {
pid,
output: [stdout, stderr],
stdout,
stderr,
status,
signal,
} = await resultPromise;
} catch (e) {
console.error(e.stack);
// The error object also has the same properties as the result object
}
})();
API
spawnAsync
takes the same arguments as child_process.spawn
. Its options are the same as those of child_process.spawn
plus:
ignoreStdio
: whether to ignore waiting for the child process's stdio streams to close before resolving the result promise. When ignoring stdio, the returned values forstdout
andstderr
will be empty strings. The default value of this option isfalse
.
It returns a promise whose result is an object with these properties:
pid
: the process ID of the spawned child processoutput
: an array with stdout and stderr's outputstdout
: a string of what the child process wrote to stdoutstderr
: a string of what the child process wrote to stderrstatus
: the exit code of the child processsignal
: the signal (ex:SIGTERM
) used to stop the child process if it did not exit on its own
If there's an error running the child process or it exits with a non-zero status code, spawnAsync
rejects the returned promise. The Error object also has the properties listed above.
Accessing the child process
Sometimes you may want to access the child process object--for example, if you wanted to attach event handlers to stdio
or stderr
and process data as it is available instead of waiting for the process to be resolved.
You can do this by accessing .child
on the Promise that is returned by spawnAsync
.
Here is an example:
(async () => {
let ffmpeg$ = spawnAsync('ffmpeg', ['-i', 'path/to/source.flac', '-codec:a', 'libmp3lame', '-b:a', '320k', '-ar', '44100', 'path/to/output.mp3']);
let childProcess = ffmpeg$.child;
childProcess.stdout.on('data', (data) => {
console.log(`ffmpeg stdout: ${data}`);
});
childProcess.stderr.on('data', (data) => {
console.error(`ffmpeg stderr: ${data}`);
});
let result = await ffmpeg$;
console.log(`ffmpeg pid ${result.pid} exited with code ${result.code}`);
})();