num = 271021678 function encode(n, arr = []) { if(n > 0) { d = n % 10 return encode((n - d)/10, [d].concat(arr)) } else { return arr.map(i => String.fromCharCode(i + 100)).join('') } } encoded = encode(num) console.log(encoded) function decode(text) { return parseInt(text.toLowerCase().split('').map(c => c.charCodeAt(0) - 100).join('')) } console.log(decode(encoded))