All notable changes to this project will be documented in this file. See [standard-version](https://github.com/conventional-changelog/standard-version) for commit guidelines.
* \_\_proto\_\_ will now be replaced with \_\_\_proto\_\_\_ in parse ([#258](https://www.github.com/yargs/yargs-parser/issues/258)), patching a potential
prototype pollution vulnerability. This was reported by the Snyk Security Research Team.([63810ca](https://www.github.com/yargs/yargs-parser/commit/63810ca1ae1a24b08293a4d971e70e058c7a41e2))
* the narg count is now enforced when parsing arrays.
### Features
* NaN can now be provided as a value for nargs, indicating "at least" one value is expected for array ([#251](https://www.github.com/yargs/yargs-parser/issues/251)) ([9db4be8](https://www.github.com/yargs/yargs-parser/commit/9db4be81417a2c7097128db34d86fe70ef4af70c))
* normalized keys were not enumerable ([#247](https://www.github.com/yargs/yargs-parser/issues/247)) ([57119f9](https://www.github.com/yargs/yargs-parser/commit/57119f9f17cf27499bd95e61c2f72d18314f11ba))
* this reverts parsing behavior of booleans to that of yargs@14
* objects used during parsing are now created with a null
prototype. There may be some scenarios where this change in behavior
leaks externally.
### Features
* boolean arguments will not be collected into an implicit array ([#236](https://www.github.com/yargs/yargs-parser/issues/236)) ([34c4e19](https://www.github.com/yargs/yargs-parser/commit/34c4e19bae4e7af63e3cb6fa654a97ed476e5eb5))
* address bugs with "uknown-options-as-args" ([bc023e3](https://www.github.com/yargs/yargs-parser/commit/bc023e3b13e20a118353f9507d1c999bf388a346))
* array should take precedence over nargs, but enforce nargs ([#243](https://www.github.com/yargs/yargs-parser/issues/243)) ([4cbc188](https://www.github.com/yargs/yargs-parser/commit/4cbc188b7abb2249529a19c090338debdad2fe6c))
* support keys that collide with object prototypes ([#234](https://www.github.com/yargs/yargs-parser/issues/234)) ([1587b6d](https://www.github.com/yargs/yargs-parser/commit/1587b6d91db853a9109f1be6b209077993fee4de))
* unknown options terminated with digits now handled by unknown-options-as-args ([#238](https://www.github.com/yargs/yargs-parser/issues/238)) ([d36cdfa](https://www.github.com/yargs/yargs-parser/commit/d36cdfa854254d7c7e0fe1d583818332ac46c2a5))
* populate error if incompatible narg/count or array/count options are used (#191)
### Features
* options that have had their default value used are now tracked ([#211](https://www.github.com/yargs/yargs-parser/issues/211)) ([a525234](https://www.github.com/yargs/yargs-parser/commit/a525234558c847deedd73f8792e0a3b77b26e2c0))
* populate error if incompatible narg/count or array/count options are used ([#191](https://www.github.com/yargs/yargs-parser/issues/191)) ([84a401f](https://www.github.com/yargs/yargs-parser/commit/84a401f0fa3095e0a19661670d1570d0c3b9d3c9))
* rework `collect-unknown-options` into `unknown-options-as-args`, providing more comprehensive functionality ([ef771ca](https://github.com/yargs/yargs-parser/commit/ef771ca))
### BREAKING CHANGES
* rework `collect-unknown-options` into `unknown-options-as-args`, providing more comprehensive functionality
* boolean arrays with default values ([#185](https://github.com/yargs/yargs-parser/issues/185)) ([7d42572](https://github.com/yargs/yargs-parser/commit/7d42572))
* boolean now behaves the same as other array types ([#184](https://github.com/yargs/yargs-parser/issues/184)) ([17ca3bd](https://github.com/yargs/yargs-parser/commit/17ca3bd))
* eatNargs() for 'opt.narg === 0' and boolean typed options ([#188](https://github.com/yargs/yargs-parser/issues/188)) ([c5a1db0](https://github.com/yargs/yargs-parser/commit/c5a1db0))
* maybeCoerceNumber now takes precedence over coerce return value ([#182](https://github.com/yargs/yargs-parser/issues/182)) ([2f26436](https://github.com/yargs/yargs-parser/commit/2f26436))
* take into account aliases when appending arrays from config object ([#199](https://github.com/yargs/yargs-parser/issues/199)) ([f8a2d3f](https://github.com/yargs/yargs-parser/commit/f8a2d3f))
### Features
* add configuration option to "collect-unknown-options" ([#181](https://github.com/yargs/yargs-parser/issues/181)) ([7909cc4](https://github.com/yargs/yargs-parser/commit/7909cc4))
* maybeCoerceNumber() now takes into account arrays ([#187](https://github.com/yargs/yargs-parser/issues/187)) ([31c204b](https://github.com/yargs/yargs-parser/commit/31c204b))
### BREAKING CHANGES
* unless "parse-numbers" is set to "false", arrays of numeric strings are now parsed as numbers, rather than strings.
* we have dropped the broken "defaulted" functionality; we would like to revisit adding this in the future.
* maybeCoerceNumber now takes precedence over coerce return value (#182)
* convert values to strings when tokenizing ([#167](https://www.github.com/yargs/yargs-parser/issues/167)) ([57b7883](https://www.github.com/yargs/yargs-parser/commit/57b7883))
* nargs should allow duplicates when duplicate-arguments-array=false ([#164](https://www.github.com/yargs/yargs-parser/issues/164)) ([47ccb0b](https://www.github.com/yargs/yargs-parser/commit/47ccb0b))
* should populate "_" when given config with "short-option-groups" false ([#179](https://www.github.com/yargs/yargs-parser/issues/179)) ([6055974](https://www.github.com/yargs/yargs-parser/commit/6055974))
* add `strip-aliased` and `strip-dashed` configuration options. ([#172](https://github.com/yargs/yargs-parser/issues/172)) ([a3936aa](https://github.com/yargs/yargs-parser/commit/a3936aa))
* support boolean which do not consume next argument. ([#171](https://github.com/yargs/yargs-parser/issues/171)) ([0ae7fcb](https://github.com/yargs/yargs-parser/commit/0ae7fcb))
* don't coerce number from string with leading '0' or '+' ([#158](https://github.com/yargs/yargs-parser/issues/158)) ([18d0fd5](https://github.com/yargs/yargs-parser/commit/18d0fd5))
### BREAKING CHANGES
* options with leading '+' or '0' now parse as strings
* better handling of quoted strings ([#153](https://github.com/yargs/yargs-parser/issues/153)) ([2fb71b2](https://github.com/yargs/yargs-parser/commit/2fb71b2))
### Features
* default value is now used if no right-hand value provided for numbers/strings ([#156](https://github.com/yargs/yargs-parser/issues/156)) ([5a7c46a](https://github.com/yargs/yargs-parser/commit/5a7c46a))
### BREAKING CHANGES
* a flag with no right-hand value no longer populates defaulted options with `undefined`.
* quotes at beginning and endings of strings are not removed during parsing.
* ensure empty string is added into argv._ ([#140](https://github.com/yargs/yargs-parser/issues/140)) ([79cda98](https://github.com/yargs/yargs-parser/commit/79cda98))
### Reverts
* make requiresArg work in conjunction with arrays ([#136](https://github.com/yargs/yargs-parser/issues/136)) ([f4a3063](https://github.com/yargs/yargs-parser/commit/f4a3063))
* handling of one char alias ([#139](https://github.com/yargs/yargs-parser/issues/139)) ([ee56e31](https://github.com/yargs/yargs-parser/commit/ee56e31))
* flatten-duplicate-arrays:false for more than 2 arrays ([#128](https://github.com/yargs/yargs-parser/issues/128)) ([2bc395f](https://github.com/yargs/yargs-parser/commit/2bc395f))
* make requiresArg work in conjunction with arrays ([#136](https://github.com/yargs/yargs-parser/issues/136)) ([77ae1d4](https://github.com/yargs/yargs-parser/commit/77ae1d4))
* also add camelCase array options ([#125](https://github.com/yargs/yargs-parser/issues/125)) ([08c0117](https://github.com/yargs/yargs-parser/commit/08c0117))
* array.type can now be provided, supporting coercion ([#132](https://github.com/yargs/yargs-parser/issues/132)) ([4b8cfce](https://github.com/yargs/yargs-parser/commit/4b8cfce))
### BREAKING CHANGES
* drops Node 4 support
* the argv object is now populated differently (correctly) when hyphens and dot notation are used in conjunction.
* do not set boolean flags if not defined in `argv` ([#119](https://github.com/yargs/yargs-parser/issues/119)) ([f6e6599](https://github.com/yargs/yargs-parser/commit/f6e6599))
### BREAKING CHANGES
*`boolean` flags defined without a `default` value will now behave like other option type and won't be set in the parsed results when the user doesn't set the corresponding CLI arg.
Previous behavior:
```js
var parse = require('yargs-parser');
parse('--flag', {boolean: ['flag']});
// => { _: [], flag: true }
parse('--no-flag', {boolean: ['flag']});
// => { _: [], flag: false }
parse('', {boolean: ['flag']});
// => { _: [], flag: false }
```
New behavior:
```js
var parse = require('yargs-parser');
parse('--flag', {boolean: ['flag']});
// => { _: [], flag: true }
parse('--no-flag', {boolean: ['flag']});
// => { _: [], flag: false }
parse('', {boolean: ['flag']});
// => { _: [] } => flag not set similarly to other option type
* narg arguments no longer consume flag arguments ([#114](https://github.com/yargs/yargs-parser/issues/114)) ([60bb9b3](https://github.com/yargs/yargs-parser/commit/60bb9b3))
### BREAKING CHANGES
* arguments of form --foo, -abc, will no longer be consumed by nargs
* tokenizer should ignore spaces at the beginning of the argString ([#106](https://github.com/yargs/yargs-parser/issues/106)) ([f34ead9](https://github.com/yargs/yargs-parser/commit/f34ead9))
### Features
* make combining arrays a configurable option ([#111](https://github.com/yargs/yargs-parser/issues/111)) ([c8bf536](https://github.com/yargs/yargs-parser/commit/c8bf536))
* merge array from arguments with array from config ([#83](https://github.com/yargs/yargs-parser/issues/83)) ([806ddd6](https://github.com/yargs/yargs-parser/commit/806ddd6))
* Ignore multiple spaces between arguments. ([#100](https://github.com/yargs/yargs-parser/issues/100)) ([d137227](https://github.com/yargs/yargs-parser/commit/d137227))
### Features
* allow configuration of prefix for boolean negation ([#94](https://github.com/yargs/yargs-parser/issues/94)) ([00bde7d](https://github.com/yargs/yargs-parser/commit/00bde7d))
* reworking how numbers are parsed ([#104](https://github.com/yargs/yargs-parser/issues/104)) ([fba00eb](https://github.com/yargs/yargs-parser/commit/fba00eb))
### BREAKING CHANGES
* strings that fail `Number.isSafeInteger()` are no longer coerced into numbers.
* default '--' to undefined when not provided; this is closer to the array API ([#90](https://github.com/yargs/yargs-parser/issues/90)) ([4e739cc](https://github.com/yargs/yargs-parser/commit/4e739cc))
* environment variables should take precedence over config file ([#81](https://github.com/yargs/yargs-parser/issues/81)) ([76cee1f](https://github.com/yargs/yargs-parser/commit/76cee1f))
* parsing hints should apply for dot notation keys ([#86](https://github.com/yargs/yargs-parser/issues/86)) ([3e47d62](https://github.com/yargs/yargs-parser/commit/3e47d62))
### Chores
* upgrade to newest version of camelcase ([#87](https://github.com/yargs/yargs-parser/issues/87)) ([f1903aa](https://github.com/yargs/yargs-parser/commit/f1903aa))
### Features
* add -- option which allows arguments after the -- flag to be returned separated from positional arguments ([#84](https://github.com/yargs/yargs-parser/issues/84)) ([2572ca8](https://github.com/yargs/yargs-parser/commit/2572ca8))
* when parsing stops, we now populate "--" by default ([#88](https://github.com/yargs/yargs-parser/issues/88)) ([cd666db](https://github.com/yargs/yargs-parser/commit/cd666db))
### BREAKING CHANGES
* rather than placing arguments in "_", when parsing is stopped via "--"; we now populate an array called "--" by default.
* camelcase now requires Node 4+.
* environment variables will now override config files (args, env, config-file, config-object)
* environment variables should take precedence over config file ([#81](https://github.com/yargs/yargs-parser/issues/81)) ([76cee1f](https://github.com/yargs/yargs-parser/commit/76cee1f))
### BREAKING CHANGES
* environment variables will now override config files (args, env, config-file, config-object)
* inner objects in configs had their keys appended to top-level key when dot-notation was disabled ([#72](https://github.com/yargs/yargs-parser/issues/72)) ([0b1b5f9](https://github.com/yargs/yargs-parser/commit/0b1b5f9))
### Features
* allow multiple arrays to be provided, rather than always combining ([#71](https://github.com/yargs/yargs-parser/issues/71)) ([0f0fb2d](https://github.com/yargs/yargs-parser/commit/0f0fb2d))
* coerce should be applied to the final objects and arrays created ([#57](https://github.com/yargs/yargs-parser/issues/57)) ([4ca69da](https://github.com/yargs/yargs-parser/commit/4ca69da))
### BREAKING CHANGES
* coerce is no longer applied to individual arguments in an implicit array.
* coerce full array instead of each element ([#51](https://github.com/yargs/yargs-parser/issues/51)) ([cc4dc56](https://github.com/yargs/yargs-parser/commit/cc4dc56))
* parsing issue with numeric character in group of options ([#19](https://github.com/yargs/yargs-parser/issues/19)) ([f743236](https://github.com/yargs/yargs-parser/commit/f743236))
* **count:** do not increment a default value ([#39](https://github.com/yargs/yargs-parser/issues/39)) ([b04a189](https://github.com/yargs/yargs-parser/commit/b04a189))
* **boolean:** fix for boolean options with non boolean defaults (#20) ([2dbe86b](https://github.com/yargs/yargs-parser/commit/2dbe86b)), closes [(#20](https://github.com/(/issues/20)
* **package:** remove tests from tarball ([0353c0d](https://github.com/yargs/yargs-parser/commit/0353c0d))
* **parsing:** handle calling short option with an empty string as the next value. ([a867165](https://github.com/yargs/yargs-parser/commit/a867165))
* boolean flag when next value contains the strings 'true' or 'false'. ([69941a6](https://github.com/yargs/yargs-parser/commit/69941a6))
* update dependencies; add standard-version bin for next release (#24) ([822d9d5](https://github.com/yargs/yargs-parser/commit/822d9d5))
### Features
* **configuration:** Allow to pass configuration objects to yargs-parser ([0780900](https://github.com/yargs/yargs-parser/commit/0780900))
* **normalize:** allow normalize to work with arrays ([e0eaa1a](https://github.com/yargs/yargs-parser/commit/e0eaa1a))
