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

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An ES2019 spec-compliant `Array.prototype.flat` 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 proposed [spec](https://tc39.github.io/proposal-flatMap/).

Because `Array.prototype.flat` 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.flat
```

## Usage/Examples

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

var arr = [1, [2], [], 3, [[4]]];

assert.deepEqual(flat(arr, 1), [1, 2, 3, [4]]);
```

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

assert.equal(shimmedFlat, flat.getPolyfill());
assert.deepEqual(arr.flat(), flat(arr));
```

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

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

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

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

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