```
const decode = cipher => {
let result = ''
for(let i = 0; i < cipher.length; i+=4) {
const a = codeTable.indexOf(cipher[i])
const b = codeTable.indexOf(cipher[i+1])
const c = codeTable.indexOf(cipher[i+2])
const d = codeTable.indexOf(cipher[i+3])

const n1 = a << 2 | b >> 4
const n2 = (b & 15) << 4 | c >> 2
const n3 = (c & 3) << 6 | d
result += String.fromCharCode(n1)
if(c != 64) {
result += String.fromCharCode(n2)
}
if(d != 64) {
result += String.fromCharCode(n3)
}
}
return result
}
```