const fs = require('fs'); const dict = fs.readdirSync('./domains').map(f => [ f.split('.').slice(0, -1).join('.'), JSON.parse(fs.readFileSync(`./domains/${f}`, 'utf8')).owner.username // owner ]).reduce((v, [s, o]) => { if (!v[o]) v[o] = []; v[o].push(s); return v; }, {}); console.log(JSON.stringify(dict));