PHP's array_merge_recursive in JavaScript

Here’s what our current JavaScript equivalent to PHP's array_merge_recursive looks like.

module.exports = function array_merge_recursive (arr1, arr2) { // eslint-disable-line camelcase
// discuss at:
// original by: Subhasis Deb
// input by: Brett Zamir (
// bugfixed by: Kevin van Zonneveld (
// example 1: var $arr1 = {'color': {'favorite': 'red'}, 0: 5}
// example 1: var $arr2 = {0: 10, 'color': {'favorite': 'green', 0: 'blue'}}
// example 1: array_merge_recursive($arr1, $arr2)
// returns 1: {'color': {'favorite': {0: 'red', 1: 'green'}, 0: 'blue'}, 1: 5, 1: 10}
// test: skip-1
const arrayMerge = require('../array/array_merge')
let idx = ''
if (arr1 && === '[object Array]' &&
arr2 && === '[object Array]') {
for (idx in arr2) {
} else if ((arr1 && (arr1 instanceof Object)) && (arr2 && (arr2 instanceof Object))) {
for (idx in arr2) {
if (idx in arr1) {
if (typeof arr1[idx] === 'object' && typeof arr2 === 'object') {
arr1[idx] = arrayMerge(arr1[idx], arr2[idx])
} else {
arr1[idx] = arr2[idx]
} else {
arr1[idx] = arr2[idx]
return arr1
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How to use

You you can install via npm install locutus and require it via require('locutus/php/array/array_merge_recursive'). You could also require the array module in full so that you could access array.array_merge_recursive instead.

If you intend to target the browser, you can then use a module bundler such as Parcel, webpack, Browserify, or rollup.js. This can be important because Locutus allows modern JavaScript in the source files, meaning it may not work in all browsers without a build/transpile step. Locutus does transpile all functions to ES5 before publishing to npm.

PHP arrays and JavaScript

Please note that Locutus uses JavaScript objects as substitutes for PHP arrays, they are the closest we can get to this hashtable-like data structure without rolling our own. While many JavaScript implementations preserve the order of object properties, the ECMAScript Language Specification explicitly states that:

The mechanics and order of enumerating the properties is not specified.

So don't use this for anything serious if you rely on the order to be consistent accross platforms.

A community effort

Not unlike Wikipedia, Locutus is an ongoing community effort. Our philosophy follows The McDonald’s Theory. This means that we don't consider it to be a bad thing that many of our functions are first iterations, which may still have their fair share of issues. We hope that these flaws will inspire others to come up with better ideas.

This way of working also means that we don't offer any production guarantees, and recommend to use Locutus inspiration and learning purposes only.


Please note that these examples are distilled from test cases that automatically verify our functions still work correctly. This could explain some quirky ones.

#codeexpected result
1var $arr1 = {'color': {'favorite': 'red'}, 0: 5} var $arr2 = {0: 10, 'color': {'favorite': 'green', 0: 'blue'}} array_merge_recursive($arr1, $arr2){'color': {'favorite': {0: 'red', 1: 'green'}, 0: 'blue'}, 1: 5, 1: 10}

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