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))