base62

Base62 encoder/decoder

Installation

npm install --save @fry/base62

Usage

encode() expects data that can be turned into a Buffer (e.g. a string,
an Array, ArrayBuffer, or a Buffer) and it returns the Base62 encoded
string.

decode() returns the decoded data in a Buffer which has good readers for
binary data as well as a fast toString() that can return the data encoded
in utf8 (default), base64, hex, etc.

$3

``javascript
const base62 = require('@fry/base62');

const encoded = base62.encode([0x2a, 0x2a]);
// encoded => AYA

const decoded = base62.decode(encoded);
// decoded =>

decoded[0]; // => 0x2a
decoded.readUInt16BE(); // => 0x2a2a
`

$3

`javascript
const encoded = base62.encode('Memento vivere');
// encoded => JMLjPMvqRo1sQNPbSc5

const decoded = base62.decode(encoded);
// decoded =>

decoded.toString(); // => Memento vivere
`

$3

There is no standard for Base62 encoding so various encoders may use different
symbol tables. This module will by default use alphanumerical characters in
their natural order: 0-9A-Za-z.

To use another set of characters first initiate them with prepareSymbolTable()
and then supply the resulting object as a second parameter to the encode/decode
functions, e.g.:

`javascript
const symbols = base62.prepareSymbolTable('ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789');
const encoded = base62.encode([0x53, 0xfe, 0x92], symbols);
// encoded => U98kC

const decoded = base62.decode(encoded, symbols);
// decoded =>
``

Base62 encoding process

The Base62 symbol table is limited to 62 characters, which is just shy of 6 bits
of information. This means that special care needs to be taken in order to encode
any given stream of bytes. This module takes the approach of reading a sextet
(6-bit chunk) from the binary stream and encode it into the symbol table as long
as the chunk is not in risk of overflowing. If the sextet is in the ”overflow
zone“ then only 5 bits are used while encoding that particular chunk, indicated
in the output by the presence of one of the symbol table’s last two characters.
The overflow bit is left in the stream until the next sextet will be read. The
last chunk may also be left-padded with zeroes during the encoding process which
the decoder will detect and reverse to ensure byte-alignment of the underlying
binary stream.

Happy encoding!

/ Fry