# fill-range [](https://www.paypal.com/cgi-bin/webscr?cmd=_s-xclick&hosted_button_id=W8YFZ425KND68) [](https://www.npmjs.com/package/fill-range) [](https://npmjs.org/package/fill-range) [](https://npmjs.org/package/fill-range) [](https://travis-ci.org/jonschlinkert/fill-range)
> Fill in a range of numbers or letters, optionally passing an increment or `step` to use, or create a regex-compatible range with `options.toRegex`
Please consider following this project's author, [Jon Schlinkert](https://github.com/jonschlinkert), and consider starring the project to show your :heart: and support.
## Install
Install with [npm](https://www.npmjs.com/):
```sh
$ npm install --save fill-range
```
## Usage
Expands numbers and letters, optionally using a `step` as the last argument. _(Numbers may be defined as JavaScript numbers or strings)_.
```js
const fill = require('fill-range');
// fill(from, to[, step, options]);
console.log(fill('1', '10')); //=> ['1', '2', '3', '4', '5', '6', '7', '8', '9', '10']
console.log(fill('1', '10', { toRegex: true })); //=> [1-9]|10
```
**Params**
* `from`: **{String|Number}** the number or letter to start with
* `to`: **{String|Number}** the number or letter to end with
* `step`: **{String|Number|Object|Function}** Optionally pass a [step](#optionsstep) to use.
* `options`: **{Object|Function}**: See all available [options](#options)
## Examples
By default, an array of values is returned.
**Alphabetical ranges**
```js
console.log(fill('a', 'e')); //=> ['a', 'b', 'c', 'd', 'e']
console.log(fill('A', 'E')); //=> [ 'A', 'B', 'C', 'D', 'E' ]
```
**Numerical ranges**
Numbers can be defined as actual numbers or strings.
```js
console.log(fill(1, 5)); //=> [ 1, 2, 3, 4, 5 ]
console.log(fill('1', '5')); //=> [ 1, 2, 3, 4, 5 ]
```
**Negative ranges**
Numbers can be defined as actual numbers or strings.
```js
console.log(fill('-5', '-1')); //=> [ '-5', '-4', '-3', '-2', '-1' ]
console.log(fill('-5', '5')); //=> [ '-5', '-4', '-3', '-2', '-1', '0', '1', '2', '3', '4', '5' ]
```
**Steps (increments)**
```js
// numerical ranges with increments
console.log(fill('0', '25', 4)); //=> [ '0', '4', '8', '12', '16', '20', '24' ]
console.log(fill('0', '25', 5)); //=> [ '0', '5', '10', '15', '20', '25' ]
console.log(fill('0', '25', 6)); //=> [ '0', '6', '12', '18', '24' ]
// alphabetical ranges with increments
console.log(fill('a', 'z', 4)); //=> [ 'a', 'e', 'i', 'm', 'q', 'u', 'y' ]
console.log(fill('a', 'z', 5)); //=> [ 'a', 'f', 'k', 'p', 'u', 'z' ]
console.log(fill('a', 'z', 6)); //=> [ 'a', 'g', 'm', 's', 'y' ]
```
## Options
### options.step
**Type**: `number` (formatted as a string or number)
**Default**: `undefined`
**Description**: The increment to use for the range. Can be used with letters or numbers.
**Example(s)**
```js
// numbers
console.log(fill('1', '10', 2)); //=> [ '1', '3', '5', '7', '9' ]
console.log(fill('1', '10', 3)); //=> [ '1', '4', '7', '10' ]
console.log(fill('1', '10', 4)); //=> [ '1', '5', '9' ]
// letters
console.log(fill('a', 'z', 5)); //=> [ 'a', 'f', 'k', 'p', 'u', 'z' ]
console.log(fill('a', 'z', 7)); //=> [ 'a', 'h', 'o', 'v' ]
console.log(fill('a', 'z', 9)); //=> [ 'a', 'j', 's' ]
```
### options.strictRanges
**Type**: `boolean`
**Default**: `false`
**Description**: By default, `null` is returned when an invalid range is passed. Enable this option to throw a `RangeError` on invalid ranges.
**Example(s)**
The following are all invalid:
```js
fill('1.1', '2'); // decimals not supported in ranges
fill('a', '2'); // incompatible range values
fill(1, 10, 'foo'); // invalid "step" argument
```
### options.stringify
**Type**: `boolean`
**Default**: `undefined`
**Description**: Cast all returned values to strings. By default, integers are returned as numbers.
**Example(s)**
```js
console.log(fill(1, 5)); //=> [ 1, 2, 3, 4, 5 ]
console.log(fill(1, 5, { stringify: true })); //=> [ '1', '2', '3', '4', '5' ]
```
### options.toRegex
**Type**: `boolean`
**Default**: `undefined`
**Description**: Create a regex-compatible source string, instead of expanding values to an array.
**Example(s)**
```js
// alphabetical range
console.log(fill('a', 'e', { toRegex: true })); //=> '[a-e]'
// alphabetical with step
console.log(fill('a', 'z', 3, { toRegex: true })); //=> 'a|d|g|j|m|p|s|v|y'
// numerical range
console.log(fill('1', '100', { toRegex: true })); //=> '[1-9]|[1-9][0-9]|100'
// numerical range with zero padding
console.log(fill('000001', '100000', { toRegex: true }));
//=> '0{5}[1-9]|0{4}[1-9][0-9]|0{3}[1-9][0-9]{2}|0{2}[1-9][0-9]{3}|0[1-9][0-9]{4}|100000'
```
### options.transform
**Type**: `function`
**Default**: `undefined`
**Description**: Customize each value in the returned array (or [string](#optionstoRegex)). _(you can also pass this function as the last argument to `fill()`)_.
**Example(s)**
```js
// add zero padding
console.log(fill(1, 5, value => String(value).padStart(4, '0')));
//=> ['0001', '0002', '0003', '0004', '0005']
```
## About
<details>
<summary><strong>Contributing</strong></summary>
Pull requests and stars are always welcome. For bugs and feature requests, [please create an issue](../../issues/new).
</details>
<details>
<summary><strong>Running Tests</strong></summary>
Running and reviewing unit tests is a great way to get familiarized with a library and its API. You can install dependencies and run tests with the following command:
```sh
$ npm install && npm test
```
</details>
<details>
<summary><strong>Building docs</strong></summary>
_(This project's readme.md is generated by [verb](https://github.com/verbose/verb-generate-readme), please don't edit the readme directly. Any changes to the readme must be made in the [.verb.md](.verb.md) readme template.)_
To generate the readme, run the following command:
```sh
$ npm install -g verbose/verb#dev verb-generate-readme && verb
```
</details>
### Contributors
| **Commits** | **Contributor** |
| --- | --- |
| 116 | [jonschlinkert](https://github.com/jonschlinkert) |
| 4 | [paulmillr](https://github.com/paulmillr) |
| 2 | [realityking](https://github.com/realityking) |
| 2 | [bluelovers](https://github.com/bluelovers) |
| 1 | [edorivai](https://github.com/edorivai) |
| 1 | [wtgtybhertgeghgtwtg](https://github.com/wtgtybhertgeghgtwtg) |
### Author
**Jon Schlinkert**
* [GitHub Profile](https://github.com/jonschlinkert)
* [Twitter Profile](https://twitter.com/jonschlinkert)
* [LinkedIn Profile](https://linkedin.com/in/jonschlinkert)
Please consider supporting me on Patreon, or [start your own Patreon page](https://patreon.com/invite/bxpbvm)!
<a href="https://www.patreon.com/jonschlinkert">
<img src="https://c5.patreon.com/external/logo/become_a_patron_button@2x.png" height="50">
</a>
### License
Copyright © 2019, [Jon Schlinkert](https://github.com/jonschlinkert).
Released under the [MIT License](LICENSE).
***
_This file was generated by [verb-generate-readme](https://github.com/verbose/verb-generate-readme), v0.8.0, on April 08, 2019._
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