import { ufs } from 'unionfs';
import { fs as fs1 } from 'memfs';
import * as fs2 from 'fs';

ufs.use(fs1).use(fs2);

ufs.readFileSync(/* ... */);

import * as fs from 'fs';
import { Volume } from 'memfs';
import * as MemoryFileSystem from 'memory-fs';
import { ufs } from 'unionfs';

const vol1 = Volume.fromJSON({ '/memfs-1': '1' });
const vol2 = Volume.fromJSON({ '/memfs-2': '2' });

const memoryFs = new MemoryFileSystem();
memoryFs.writeFileSync('/memory-fs', '3');

ufs.use(fs).use(vol1).use(vol2).use(memoryFs);

console.log(ufs.readFileSync('/memfs-1', 'utf8')); // 1
console.log(ufs.readFileSync('/memfs-2', 'utf8')); // 2
console.log(ufs.readFileSync('/memory-fs', 'utf8')); // 3

import { Union } from 'unionfs';

var ufs1 = new Union();
ufs1.use(fs).use(vol);

var ufs2 = new Union();
ufs2.use(fs).use(/*...*/);