string
* [.type](#module_option-definition--OptionDefinition+type) : function
* [.alias](#module_option-definition--OptionDefinition+alias) : string
* [.multiple](#module_option-definition--OptionDefinition+multiple) : boolean
* [.lazyMultiple](#module_option-definition--OptionDefinition+lazyMultiple) : boolean
* [.defaultOption](#module_option-definition--OptionDefinition+defaultOption) : boolean
* [.defaultValue](#module_option-definition--OptionDefinition+defaultValue) : \*
* [.group](#module_option-definition--OptionDefinition+group) : string \| Array.<string>
### OptionDefinition ⏏
Describes a command-line option. Additionally, if generating a usage guide with [command-line-usage](https://github.com/75lb/command-line-usage) you could optionally add `description` and `typeLabel` properties to each definition.
**Kind**: Exported class
#### option.name : string
The only required definition property is `name`, so the simplest working example is
```js
const optionDefinitions = [
{ name: 'file' },
{ name: 'depth' }
]
```
Where a `type` property is not specified it will default to `String`.
| # | Command line args | .parse() output |
| --- | -------------------- | ------------ |
| 1 | `--file` | `{ file: null }` |
| 2 | `--file lib.js` | `{ file: 'lib.js' }` |
| 3 | `--depth 2` | `{ depth: '2' }` |
Unicode option names and aliases are valid, for example:
```js
const optionDefinitions = [
{ name: 'один' },
{ name: '两' },
{ name: 'три', alias: 'т' }
]
```
**Kind**: instance property of [OptionDefinition](#exp_module_option-definition--OptionDefinition)
#### option.type : function
The `type` value is a setter function (you receive the output from this), enabling you to be specific about the type and value received.
The most common values used are `String` (the default), `Number` and `Boolean` but you can use a custom function, for example:
```js
const fs = require('fs')
class FileDetails {
constructor (filename) {
this.filename = filename
this.exists = fs.existsSync(filename)
}
}
const cli = commandLineArgs([
{ name: 'file', type: filename => new FileDetails(filename) },
{ name: 'depth', type: Number }
])
```
| # | Command line args| .parse() output |
| --- | ----------------- | ------------ |
| 1 | `--file asdf.txt` | `{ file: { filename: 'asdf.txt', exists: false } }` |
The `--depth` option expects a `Number`. If no value was set, you will receive `null`.
| # | Command line args | .parse() output |
| --- | ----------------- | ------------ |
| 2 | `--depth` | `{ depth: null }` |
| 3 | `--depth 2` | `{ depth: 2 }` |
**Kind**: instance property of [OptionDefinition](#exp_module_option-definition--OptionDefinition)
**Default**: String
#### option.alias : string
getopt-style short option names. Can be any single character (unicode included) except a digit or hyphen.
```js
const optionDefinitions = [
{ name: 'hot', alias: 'h', type: Boolean },
{ name: 'discount', alias: 'd', type: Boolean },
{ name: 'courses', alias: 'c' , type: Number }
]
```
| # | Command line | .parse() output |
| --- | ------------ | ------------ |
| 1 | `-hcd` | `{ hot: true, courses: null, discount: true }` |
| 2 | `-hdc 3` | `{ hot: true, discount: true, courses: 3 }` |
**Kind**: instance property of [OptionDefinition](#exp_module_option-definition--OptionDefinition)
#### option.multiple : boolean
Set this flag if the option takes a list of values. You will receive an array of values, each passed through the `type` function (if specified).
```js
const optionDefinitions = [
{ name: 'files', type: String, multiple: true }
]
```
Note, examples 1 and 3 below demonstrate "greedy" parsing which can be disabled by using `lazyMultiple`.
| # | Command line | .parse() output |
| --- | ------------ | ------------ |
| 1 | `--files one.js two.js` | `{ files: [ 'one.js', 'two.js' ] }` |
| 2 | `--files one.js --files two.js` | `{ files: [ 'one.js', 'two.js' ] }` |
| 3 | `--files *` | `{ files: [ 'one.js', 'two.js' ] }` |
**Kind**: instance property of [OptionDefinition](#exp_module_option-definition--OptionDefinition)
#### option.lazyMultiple : boolean
Identical to `multiple` but with greedy parsing disabled.
```js
const optionDefinitions = [
{ name: 'files', lazyMultiple: true },
{ name: 'verbose', alias: 'v', type: Boolean, lazyMultiple: true }
]
```
| # | Command line | .parse() output |
| --- | ------------ | ------------ |
| 1 | `--files one.js --files two.js` | `{ files: [ 'one.js', 'two.js' ] }` |
| 2 | `-vvv` | `{ verbose: [ true, true, true ] }` |
**Kind**: instance property of [OptionDefinition](#exp_module_option-definition--OptionDefinition)
#### option.defaultOption : boolean
Any values unaccounted for by an option definition will be set on the `defaultOption`. This flag is typically set on the most commonly-used option to make for more concise usage (i.e. `$ example *.js` instead of `$ example --files *.js`).
```js
const optionDefinitions = [
{ name: 'files', multiple: true, defaultOption: true }
]
```
| # | Command line | .parse() output |
| --- | ------------ | ------------ |
| 1 | `--files one.js two.js` | `{ files: [ 'one.js', 'two.js' ] }` |
| 2 | `one.js two.js` | `{ files: [ 'one.js', 'two.js' ] }` |
| 3 | `*` | `{ files: [ 'one.js', 'two.js' ] }` |
**Kind**: instance property of [OptionDefinition](#exp_module_option-definition--OptionDefinition)
#### option.defaultValue : \*
An initial value for the option.
```js
const optionDefinitions = [
{ name: 'files', multiple: true, defaultValue: [ 'one.js' ] },
{ name: 'max', type: Number, defaultValue: 3 }
]
```
| # | Command line | .parse() output |
| --- | ------------ | ------------ |
| 1 | | `{ files: [ 'one.js' ], max: 3 }` |
| 2 | `--files two.js` | `{ files: [ 'two.js' ], max: 3 }` |
| 3 | `--max 4` | `{ files: [ 'one.js' ], max: 4 }` |
**Kind**: instance property of [OptionDefinition](#exp_module_option-definition--OptionDefinition)
#### option.group : string \| Array.<string>
When your app has a large amount of options it makes sense to organise them in groups.
There are two automatic groups: `_all` (contains all options) and `_none` (contains options without a `group` specified in their definition).
```js
const optionDefinitions = [
{ name: 'verbose', group: 'standard' },
{ name: 'help', group: [ 'standard', 'main' ] },
{ name: 'compress', group: [ 'server', 'main' ] },
{ name: 'static', group: 'server' },
{ name: 'debug' }
]
```
| # | Command Line | .parse() output |
|---|---|---|
| 1 | --verbose | |
| 2 | --debug | |
| 3 | --verbose --debug --compress | |
| 4 | --compress | |
OptionDefinition](#exp_module_option-definition--OptionDefinition)