array.prototype.flatmap
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Package description
The array.prototype.flatmap package provides a polyfill for the flatMap method that was added to the Array prototype in ECMAScript 2019. This method allows you to map over an array and flatten the result by one level in a single operation. It is particularly useful for dealing with arrays of arrays or when applying a function that returns an array for each element.
Mapping and Flattening
This code demonstrates how to use flatMap to map over an array of arrays, doubling each element, and then flattening the result into a single array. The output would be [2, 4, 6, 8].
[[1, 2], [3, 4]].flatMap(x => x.map(y => y * 2))Filtering and Mapping in One Step
This example shows how flatMap can be used to filter and map over an array simultaneously. It doubles the even numbers and removes the odd numbers, resulting in [4, 8].
[1, 2, 3, 4].flatMap(x => x % 2 === 0 ? [x * 2] : [])Lodash's flatten method provides similar functionality to flatMap for flattening arrays, but it does not include mapping. You would need to chain it with map for similar effects, making array.prototype.flatmap more convenient for combined operations.
Underscore.js offers methods like _.flatten and _.map which can be combined to achieve similar results to flatMap. However, like lodash, this requires chaining multiple operations, whereas array.prototype.flatmap integrates both into one method.
Changelog
v1.3.1 - 2022-11-02
npmignore to autogenerate an npmignore file 3587a34auto-changelog d66bdeadefine-properties, es-abstract d64c4868d657d0aud, object-inspect, tape aa22741for-each instead of foreach 748a78dshim/auto: add flatMap to Symbol.unscopablescall-bind, es-abstracteslint, @ljharb/eslint-config, @es-shims/api, aud, auto-changelog, object-inspect, safe-publish-latest, tapecall-bind, es-abstract; remove unused function-bindprepublishOnly, for npm 7+eslint, @ljharb/eslint-config, @es-shims/api, aud, has-strict-mode, object-inspect, tapenode/install instead of node/run; use codecov actiones-abstract; use call-bind where applicableeslint, @ljharb/eslint-config, object-inspect, tape; add audnyc on all testsimplementation test; run es-shim-api in postlint; use tape runnerpull_request_target eventes-abstract (65% bundle size decrease)es-abstracteslint, @ljharb/eslint-config, safe-publish-latest, object-inspectfunding fieldmapperFunction, to match speces-abstract, define-propertieseslint, @ljharb/eslint-config, covert, evalmd, object-inspect, safe-publish-latest, tapenode v12.11, v11.15, v10.16, v9.11, v8.16, v6.17, v4.9; use nvm install-latest-npmnpx aud instead of nsp or npm audit with hoopseslint, nsp, tapenode v9.6, v6.13eslint, object-inspectnode v9.4es-abstracteslint, nsp, object-inspectnode v9.2, v8.9, v6.12; pin included builds to LTSFlattenIntoArray: add assertion that thisArg and mapperFunction are both passed togetherReadme
An ES2019 spec-compliant Array.prototype.flatMap 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 spec.
Because Array.prototype.flatMap depends on a receiver (the this value), the main export takes the array to operate on as the first argument.
npm install --save array.prototype.flatmap
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]);
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));
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));
Simply clone the repo, npm install, and run npm test
FAQs
An ES2019 spec-compliant `Array.prototype.flatMap` shim/polyfill/replacement that works as far down as ES3.
The npm package array.prototype.flatmap receives a total of 17,989,278 weekly downloads. As such, array.prototype.flatmap popularity was classified as popular.
We found that array.prototype.flatmap 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.
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