# array.prototype.flatmap <sup>[![Version Badge][npm-version-svg]][package-url]</sup>

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An ES2019 spec-compliant `Array.prototype.flatMap` shim/polyfill/replacement that works as far down as ES3.

This package implements the [es-shim API](https://github.com/es-shims/api) interface. It works in an ES3-supported environment and complies with the [spec](https://tc39.es/ecma262/#sec-array.prototype.flatmap).

Because `Array.prototype.flatMap` depends on a receiver (the `this` value), the main export takes the array to operate on as the first argument.

## Getting started

```sh
npm install --save array.prototype.flatmap
```

## Usage/Examples

```js
var flatMap = require('array.prototype.flatmap');
var assert = require('assert');

var arr = [1, [2], [], 3];

var results = flatMap(arr, function (x, i) {
	assert.equal(x, arr[i]);
	return x;
});

assert.deepEqual(results, [1, 2, 3]);
```

```js
var flatMap = require('array.prototype.flatmap');
var assert = require('assert');
/* when Array#flatMap is not present */
delete Array.prototype.flatMap;
var shimmedFlatMap = flatMap.shim();

var mapper = function (x) { return [x, 1]; };

assert.equal(shimmedFlatMap, flatMap.getPolyfill());
assert.deepEqual(arr.flatMap(mapper), flatMap(arr, mapper));
```

```js
var flatMap = require('array.prototype.flatmap');
var assert = require('assert');
/* when Array#flatMap is present */
var shimmedIncludes = flatMap.shim();

var mapper = function (x) { return [x, 1]; };

assert.equal(shimmedIncludes, Array.prototype.flatMap);
assert.deepEqual(arr.flatMap(mapper), flatMap(arr, mapper));
```

## Tests
Simply clone the repo, `npm install`, and run `npm test`

[package-url]: https://npmjs.org/package/array.prototype.flatmap
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