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


Version published
Weekly downloads
decreased by-12.47%

Weekly downloads



v1.3.1 - 2022-11-02


  • [meta] use npmignore to autogenerate an npmignore file e339ed7
  • [meta] add auto-changelog bb5cbd6
  • [Deps] update define-properties, es-abstract 8067910
  • [actions] update rebase action to use reusable workflow d4d9b28
  • [Dev Deps] update aud, object-inspect, tape d9d7300
<!-- auto-changelog-above -->

1.3.0 / 2022-04-11

  • [New] shim/auto: add flat to Symbol.unscopables
  • [Deps] update es-abstract
  • [actions] reuse common workflows
  • [actions] update codecov uploader
  • [Dev Deps] update eslint, @ljharb/eslint-config, @es-shims/api, aud, auto-changelog, object-inspect, safe-publish-latest, tape

1.2.5 / 2021-10-01

  • [readme] add github actions/codecov badges; remove travis badge
  • [Deps] update call-bind, es-abstract
  • [Dev Deps] update eslint, @ljharb/eslint-config, @es-shims/api, aud, has-strict-mode, object-inspect, tape
  • [meta] use prepublishOnly, for npm 7+
  • [actions] use node/install instead of node/run; use codecov action
  • [actions] update workflows
  • [Tests] increase coverage
  • [meta] fix changelog for v1.2.4

1.2.4 / 2020-11-18

  • [meta] do not publish Github Action workflows
  • [Deps] update es-abstract; add call-bind where applicable
  • [Dev Deps] update eslint, @ljharb/eslint-config, aud, object-inspect, tape
  • [Tests] run nyc on all tests
  • [Tests] add implementation test; run es-shim-api in postlint; use tape runner
  • [Tests] migrate tests to Github Actions
  • [actions] add "Allow Edits" workflow
  • [actions] switch Automatic Rebase workflow to pull_request_target event

1.2.3 / 2019-12-12

  • [Refactor] use split-up es-abstract (65% bundle size decrease)
  • [Deps] update es-abstract
  • [Dev Deps] update eslint, @ljharb/eslint-config, safe-publish-latest, object-inspect
  • [meta] ESnext -> ES2019
  • [meta] add funding field
  • [Tests] use shared travis-ci configs
  • [actions] add automatic rebasing / merge commit blocking

1.2.2 / 2019-10-10

  • [Deps] update es-abstract, define-properties
  • [Dev Deps] update eslint, @ljharb/eslint-config, covert, evalmd, object-inspect, safe-publish-latest, tape
  • [meta] create FUNDING.yml
  • [Tests] use npx aud instead of nsp or npm audit with hoops
  • [Tests] up to node v12.11, v11.15, v10.16, v9.11, v8.16, v6.17, v4.9; use nvm install-latest-npm

1.2.1 / 2018-02-23

  • [Fix] Temporarily hack main entry, so it's compatible with other resolvers (#3)
  • [Dev Deps] update eslint, nsp, tape
  • [Tests] up to node v9.6, v6.13

1.2.0 / 2018-01-18

  • [New] add "auto" entry point
  • [Fix] Move the receiver length check higher
  • [Fix] spec adjustments
  • [Refactor] adjust shouldFlatten logic
  • [Dev Deps] update eslint
  • [Tests] up to node v9.4

1.1.1 / 2017-11-29

  • [Fix] avoid an extra hole in the array (
  • [Deps] update es-abstract
  • [Dev Deps] update eslint, nsp
  • [Tests] up to node v9.2, v8.9, v6.12; pin included builds to LTS.

1.1.0 / 2017-10-03

  • [New] add explicit setting of “length” on target array
  • [Fix] FlattenIntoArray: add assertion that thisArg and mapperFunction are both passed together
  • [Tests] make coverage required

1.0.1 / 2017-10-02

  • Add readme

1.0.0 / 2017-10-01

  • Initial release



array.prototype.flat Version Badge

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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 interface. It works in an ES3-supported environment and complies with the proposed spec.

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

npm install --save array.prototype.flat


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]]); 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)); 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));


Simply clone the repo, npm install, and run npm test



What is array.prototype.flat?

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

Is array.prototype.flat popular?

The npm package array.prototype.flat receives a total of 13,129,728 weekly downloads. As such, array.prototype.flat popularity was classified as popular.

Is array.prototype.flat well maintained?

We found that array.prototype.flat demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago.It has 1 open source maintainer collaborating on the project.

Last updated on 03 Nov 2022

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