Node.js: Spawn process. Keep StdOut and StdErr in the original order. Display output real time. Capture output on exit.

spawn.js

// Based on answer from https://stackoverflow.com/questions/57046930/node-js-spawn-keep-stdout-and-stderr-in-the-original-order

const { spawn } = require('child_process');

const options = {
    shell: true, // Keep shell: true to redirect StdErr to StdOut.
    stdio: [
        'inherit', // StdIn. Fixes "ERROR: Input redirection is not supported, exiting the process immediately" on Windows.
        'pipe',    // StdOut.
        'pipe',    // StdErr.
    ],
};

const child = spawn('my-executable-name', ['arg1', '2>&1'], options); // Keep 2>&1 to redirect StdErr to StdOut.

let mergedOut = '';

child.stdout.setEncoding('utf8');
child.stdout.on('data', (chunk) => {
    process.stdout.write(chunk, (_err) => { });
    mergedOut += chunk;
});

child.on('close', (_code, _signal) => {
    console.log('-'.repeat(30));
    console.log(mergedOut);
});