cdigit/README.md

Collection of check digit algorithms implemented in JavaScript

# cdigit: Check Digit Algorithms in JS

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cdigit - Collection of check digit algorithms implemented in JavaScript

## Synopsis

Node.js:

```javascript
import { luhn } from "cdigit";

// Luhn (a.k.a. Mod 10) algorithm
console.log(luhn.compute("1234")); // "4"
console.log(luhn.generate("1234")); // "12344"
console.log(luhn.validate("12344")); // true
```

Command-line:

```bash
# Damm algorithm
npx cdigit --algo damm compute 1234
npx cdigit --algo damm generate 1234
npx cdigit --algo damm validate 12340
```

## Supported Algorithms

### Generic Algorithms

| Algorithm  | cdigit name | Input string  | Check character(s) |
| ---------- | ----------- | ------------- | ------------------ |
| [Luhn]     | luhn        | Numeric (0-9) | 1 digit (0-9)      |
| [Verhoeff] | verhoeff    | Numeric (0-9) | 1 digit (0-9)      |
| [Damm]     | damm        | Numeric (0-9) | 1 digit (0-9)      |

[Luhn]: https://en.wikipedia.org/wiki/Luhn_algorithm
[Verhoeff]: https://en.wikipedia.org/wiki/Verhoeff_algorithm
[Damm]: https://en.wikipedia.org/wiki/Damm_algorithm

### [ISO/IEC 7064] Family

ISO/IEC 7064 describes eight generic check digit (character) systems for
numeric, alphabetic, and alphanumeric strings. ISO/IEC 7064 specifies two types
of systems that use the same algorithm with different parameters: Pure systems
(MOD 11-2, MOD 37-2, MOD 97-10, MOD 661-26, and MOD 1271-36) and Hybrid systems
(MOD 11,10, MOD 27,26, and MOD 37,36).

| Algorithm                 | cdigit name | Input string          | Check character(s)                  |
| ------------------------- | ----------- | --------------------- | ----------------------------------- |
| ISO/IEC 7064, MOD 11-2    | mod11_2     | Numeric (0-9)         | 1 digit or 'X' (0-9X)               |
| ISO/IEC 7064, MOD 37-2    | mod37_2     | Alphanumeric (0-9A-Z) | 1 digit, letter, or '\*' (0-9A-Z\*) |
| ISO/IEC 7064, MOD 97-10   | mod97_10    | Numeric (0-9)         | 2 digits (0-9)                      |
| ISO/IEC 7064, MOD 661-26  | mod661_26   | Alphabetic (A-Z)      | 2 letters (A-Z)                     |
| ISO/IEC 7064, MOD 1271-36 | mod1271_36  | Alphanumeric (0-9A-Z) | 2 digits or letters (0-9A-Z)        |
| ISO/IEC 7064, MOD 11,10   | mod11_10    | Numeric (0-9)         | 1 digit (0-9)                       |
| ISO/IEC 7064, MOD 27,26   | mod27_26    | Alphabetic (A-Z)      | 1 letter (A-Z)                      |
| ISO/IEC 7064, MOD 37,36   | mod37_36    | Alphanumeric (0-9A-Z) | 1 digit or letter (0-9A-Z)          |

[ISO/IEC 7064]: https://www.iso.org/standard/31531.html

### [GTIN] (Global Trade Item Number) Family

GTINs are internationally unified product identification numbers that are often
(or historically) referred to as [UPC], [EAN], [ISBN]-13, etc. GTINs have
several variations in length but share the identical check digit algorithm;
therefore, `cdigit` currently provides only one generic `gtin` object for GTINs
and other [GS1 data structures]. Note that the `gtin` object does not check the
length or semantic validity of a given GTIN string.

| Algorithm | cdigit name | Input string  | Check character(s) | Also known as             |
| --------- | ----------- | ------------- | ------------------ | ------------------------- |
| GTIN-8    | gtin        | Numeric (0-9) | 1 digit (0-9)      | EAN-8                     |
| GTIN-12   | gtin        | Numeric (0-9) | 1 digit (0-9)      | UPC, UPC-A                |
| GTIN-13   | gtin        | Numeric (0-9) | 1 digit (0-9)      | EAN, [JAN], ISBN-13, etc. |
| GTIN-14   | gtin        | Numeric (0-9) | 1 digit (0-9)      | EAN, UCC-14               |

[GTIN]: https://www.gs1.org/standards/id-keys/gtin
[UPC]: https://en.wikipedia.org/wiki/Universal_Product_Code
[EAN]: https://en.wikipedia.org/wiki/International_Article_Number
[ISBN]: https://en.wikipedia.org/wiki/International_Standard_Book_Number
[GS1 data structures]: https://www.gs1.org/standards/id-keys
[JAN]: https://en.wikipedia.org/wiki/International_Article_Number#Japanese_Article_Number

## Usage - Node.js

Load algorithm objects using the cdigit names listed in
[Supported Algorithms section](#supported-algorithms).

```javascript
import { mod97_10 } from "cdigit";
```

Algorithm objects implement the following methods:

### validate(strWithCheckChars: string): boolean

Checks if a protected string is valid per the algorithm.

```javascript
console.log(mod97_10.validate("123482")); // true
```

### generate(strWithoutCheckChars: string): string

Generates the protected string from the argument using the algorithm. The
generated string consists of the original bare string and computed check
character(s), which are combined in accordance with the algorithm.

```javascript
console.log(mod97_10.generate("1234")); // "123482"
```

### compute(strWithoutCheckChars: string): string

Generates the check character(s) from the argument using the algorithm. Unlike
`generate()`, this method returns the check character(s) only.

```javascript
console.log(mod97_10.compute("1234")); // "82"
```

### computeFromNumVals(numValsWithoutCheckChars: number[]): number[]

Generates the check character(s) from the argument using the algorithm. This
method is an alphabet-independent equivalent of `compute()`, where the return
value and argument are both represented as arrays of each digit's numerical
value.

```javascript
console.log(mod97_10.computeFromNumVals([1, 2, 3, 4])); // [8, 2]
```

See [example.js](https://npm.runkit.com/cdigit) for usage examples.

## Usage - Command-line

```
Usage: cdigit [options] [command]

Options:
  -a, --algo <name>  specify check digit algorithm by name
  -h, --help         display help for command

Commands:
  validate <string>  check if string is valid
  generate <string>  append check character(s) to string
  compute <string>   print check character(s) computed from string
```

`-a, --algo <name>` option accepts the names listed in [Supported Algorithms
section](#supported-algorithms) and defaults to `luhn` or the value of
`CDIGIT_CLI_DEFAULT_ALGO` environment variable (if set).

## License

Copyright (c) 2018-2023 LiosK

Licensed under either of

- [Apache License, Version 2.0](http://www.apache.org/licenses/LICENSE-2.0)
- [MIT license](http://opensource.org/licenses/MIT)

at your option.

## Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted
for inclusion in the work by you, as defined in the Apache-2.0 license, shall be
dual licensed as above, without any additional terms or conditions.

## See Also

- [API Documentation](https://liosk.github.io/cdigit/docs/)
- [Run tests on your browser](https://liosk.github.io/cdigit/test/)