# fill-range [![NPM version](https://img.shields.io/npm/v/fill-range.svg?style=flat)](https://www.npmjs.com/package/fill-range) [![NPM monthly downloads](https://img.shields.io/npm/dm/fill-range.svg?style=flat)](https://npmjs.org/package/fill-range)  [![NPM total downloads](https://img.shields.io/npm/dt/fill-range.svg?style=flat)](https://npmjs.org/package/fill-range) [![Linux Build Status](https://img.shields.io/travis/jonschlinkert/fill-range.svg?style=flat&label=Travis)](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`

## Table of Contents

- [Install](#install)
- [Usage](#usage)
- [Examples](#examples)
- [Options](#options)
  * [options.step](#optionsstep)
  * [options.strictRanges](#optionsstrictranges)
  * [options.stringify](#optionsstringify)
  * [options.toRegex](#optionstoregex)
  * [options.transform](#optionstransform)
- [About](#about)

_(TOC generated by [verb](https://github.com/verbose/verb) using [markdown-toc](https://github.com/jonschlinkert/markdown-toc))_

## Install

Install with [npm](https://www.npmjs.com/):

```sh
$ npm install --save fill-range
```

Install with [yarn](https://yarnpkg.com):

```sh
$ yarn add 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
var fill = require('fill-range');
fill(from, to[, step, options]);

// examples
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
// increase padding by two
var arr = fill('01', '05', function(val, a, b, step, idx, arr, options) {
  return repeat('0', (options.maxLength + 2) - val.length) + val;
});

console.log(arr);
//=> ['0001', '0002', '0003', '0004', '0005']
```

## About

### Related projects

* [braces](https://www.npmjs.com/package/braces): Fast, comprehensive, bash-like brace expansion implemented in JavaScript. Complete support for the Bash 4.3 braces… [more](https://github.com/jonschlinkert/braces) | [homepage](https://github.com/jonschlinkert/braces "Fast, comprehensive, bash-like brace expansion implemented in JavaScript. Complete support for the Bash 4.3 braces specification, without sacrificing speed.")
* [expand-range](https://www.npmjs.com/package/expand-range): Fast, bash-like range expansion. Expand a range of numbers or letters, uppercase or lowercase. See… [more](https://github.com/jonschlinkert/expand-range) | [homepage](https://github.com/jonschlinkert/expand-range "Fast, bash-like range expansion. Expand a range of numbers or letters, uppercase or lowercase. See the benchmarks. Used by micromatch.")
* [micromatch](https://www.npmjs.com/package/micromatch): Glob matching for javascript/node.js. A drop-in replacement and faster alternative to minimatch and multimatch. | [homepage](https://github.com/jonschlinkert/micromatch "Glob matching for javascript/node.js. A drop-in replacement and faster alternative to minimatch and multimatch.")
* [to-regex-range](https://www.npmjs.com/package/to-regex-range): Pass two numbers, get a regex-compatible source string for matching ranges. Validated against more than… [more](https://github.com/jonschlinkert/to-regex-range) | [homepage](https://github.com/jonschlinkert/to-regex-range "Pass two numbers, get a regex-compatible source string for matching ranges. Validated against more than 2.87 million test assertions.")

### Contributing

Pull requests and stars are always welcome. For bugs and feature requests, [please create an issue](../../issues/new).

### Contributors

| **Commits** | **Contributor** |  
| --- | --- |  
| 103 | [jonschlinkert](https://github.com/jonschlinkert) |  
| 2   | [paulmillr](https://github.com/paulmillr) |  
| 1   | [edorivai](https://github.com/edorivai) |  
| 1   | [wtgtybhertgeghgtwtg](https://github.com/wtgtybhertgeghgtwtg) |  

### Building docs

_(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
```

### Running tests

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
```

### Author

**Jon Schlinkert**

* [github/jonschlinkert](https://github.com/jonschlinkert)
* [twitter/jonschlinkert](https://twitter.com/jonschlinkert)

### License

Copyright © 2017, [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), v0.5.0, on April 23, 2017._