const fs = require('fs') fs.writeFile('a.txt', 'some text', err => { if (err) throw err fs.writeFile('b.txt', 'some more text', err => { if (err) throw err fs.writeFile('c.txt', 'even more text', err => { if (err) throw err fs.stat('a.txt', (err, statsA) => { if (err) throw err fs.stat('b.txt', (err, statsB) => { if (err) throw err fs.stat('c.txt', (err, statsC) => { if (err) throw err const totalSize = statsA.size + statsB.size + statsC.size console.log(`Total size: ${totalSize} bytes`) }) }) }) }) }) })