Posting minor alteration to work with nodejs require() - for anyone reading who isn't using experimental modules/.mjs in node - perhaps can make this a gist

[n2nco]

let fs = require('fs')

let isDockerCached;

function hasDockerEnv() {
	try {
		fs.statSync('/.dockerenv');
		return true;
	} catch {
		return false;
	}
}

function hasDockerCGroup() {
	try {
		return fs.readFileSync('/proc/self/cgroup', 'utf8').includes('docker');
	} catch {
		return false;
	}
}

module.exports = function isDocker() {
        if (isDockerCached === undefined) {
            isDockerCached = hasDockerEnv() || hasDockerCGroup();
        }
        return isDockerCached;
    }

[sindresorhus]

https://gist.github.com/sindresorhus/a39789f98801d908bbc7ff3ecc99d99c