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# base-x
[](https://www.npmjs.org/package/base-x)
[](https://travis-ci.org/cryptocoinjs/base-x)
[](https://github.com/feross/standard)
Fast base encoding / decoding of any given alphabet using bitcoin style leading
zero compression.
**WARNING:** This module is **NOT RFC3548** compliant, it cannot be used for base16 (hex), base32, or base64 encoding in a standards compliant manner.
## Example
Base58
``` javascript
var BASE58 = '123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz'
var bs58 = require('base-x')(BASE58)
var decoded = bs58.decode('5Kd3NBUAdUnhyzenEwVLy9pBKxSwXvE9FMPyR4UKZvpe6E3AgLr')
console.log(decoded)
// => Uint8Array(33) [
// 128, 237, 219, 220, 17, 104, 241, 218,
// 234, 219, 211, 228, 76, 30, 63, 143,
// 90, 40, 76, 32, 41, 247, 138, 210,
// 106, 249, 133, 131, 164, 153, 222, 91,
// 25
// ]
console.log(bs58.encode(decoded))
// => 5Kd3NBUAdUnhyzenEwVLy9pBKxSwXvE9FMPyR4UKZvpe6E3AgLr
```
### Alphabets
See below for a list of commonly recognized alphabets, and their respective base.
Base | Alphabet
------------- | -------------
2 | `01`
8 | `01234567`
11 | `0123456789a`
16 | `0123456789abcdef`
32 | `0123456789ABCDEFGHJKMNPQRSTVWXYZ`
32 | `ybndrfg8ejkmcpqxot1uwisza345h769` (z-base-32)
36 | `0123456789abcdefghijklmnopqrstuvwxyz`
58 | `123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz`
62 | `0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ`
64 | `ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/`
67 | `ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_.!~`
## How it works
It encodes octet arrays by doing long divisions on all significant digits in the
array, creating a representation of that number in the new base. Then for every
leading zero in the input (not significant as a number) it will encode as a
single leader character. This is the first in the alphabet and will decode as 8
bits. The other characters depend upon the base. For example, a base58 alphabet
packs roughly 5.858 bits per character.
This means the encoded string 000f (using a base16, 0-f alphabet) will actually decode
to 4 bytes unlike a canonical hex encoding which uniformly packs 4 bits into each
character.
While unusual, this does mean that no padding is required and it works for bases
like 43.
## LICENSE [MIT](LICENSE)
A direct derivation of the base58 implementation from [`bitcoin/bitcoin`](https://github.com/bitcoin/bitcoin/blob/f1e2f2a85962c1664e4e55471061af0eaa798d40/src/base58.cpp), generalized for variable length alphabets.
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