const obj = { 115: [26, 27, 10], 116: [26, 28, 27], 117: [26, 27, 28], 118: [10, 26, 27, 28], 119: [10, 26, 27, 28] }; const keys = Object.keys(obj); const newObj = keys.reduce((acc, item, index) => { const ids = obj[item]; ids.forEach(id => { if (acc[id]) { acc[id] = [...acc[id], keys[index]]; } else { acc[id] = [keys[index]]; } }); return acc; }, {}); console.log(newObj);