fes.js/packages/fes/src/utils/fork.js

import {
    fork
} from 'child_process';

const usedPorts = [];
let CURRENT_PORT;

export default function start({
    scriptPath
}) {
    const execArgv = process.execArgv.slice(0);
    const inspectArgvIndex = execArgv.findIndex(argv => argv.includes('--inspect-brk'),);

    if (inspectArgvIndex > -1) {
        const inspectArgv = execArgv[inspectArgvIndex];
        execArgv.splice(
            inspectArgvIndex,
            1,
            inspectArgv.replace(/--inspect-brk=(.*)/, (match, s1) => {
                let port;
                try {
                    port = parseInt(s1, 10) + 1;
                } catch (e) {
                    port = 9230; // node default inspect port plus 1.
                }
                if (usedPorts.includes(port)) {
                    port += 1;
                }
                usedPorts.push(port);
                return `--inspect-brk=${port}`;
            }),
        );
    }

    // set port to env when current port has value
    if (CURRENT_PORT) {
        // @ts-ignore
        process.env.PORT = CURRENT_PORT;
    }

    const child = fork(scriptPath, process.argv.slice(2), {
        execArgv
    });

    child.on('message', (data) => {
        const type = (data && data.type) || null;
        if (type === 'RESTART') {
            child.kill();
            start({
                scriptPath
            });
        } else if (type === 'UPDATE_PORT') {
            // set current used port
            CURRENT_PORT = data.port;
        }
        process.send && process.send(data);
    });

    return child;
}