PHP's array_merge_recursive in JavaScript

How to use

You you can install via yarn add locutus and require this function via const array_merge_recursive = require('locutus/php/array/array_merge_recursive').

It is important to use a bundler that supports tree-shaking so that you only ship the functions that you actually use to your browser, instead of all of Locutus, which is massive. Examples are: Parcel, webpack, or rollup.js. For server-side use this is typically less of a concern.

Examples

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

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

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.

To influence how Locutus treats objects to arrays, you can check out the `locutus.objectsAsArrays` setting.

Notes

• Numeric keys are renumbered starting from 0, string keys are preserved

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

module.exports = function array_merge_recursive(arr1, arr2) {
  //       discuss at: https://locutus.io/php/array_merge_recursive/
  //      original by: Subhasis Deb
  //         input by: Brett Zamir (https://brett-zamir.me)
  //      bugfixed by: Kevin van Zonneveld (https://kvz.io)
  // reimplemented by: Kevin van Zonneveld (https://kvz.io)
  //           note 1: Numeric keys are renumbered starting from 0, string keys are preserved
  //        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': ['red', 'green'], 0: 'blue'}, 0: 5, 1: 10}

  const result = {}
  const toStr = Object.prototype.toString
  let numericIdx = 0

  // Helper to check if a key is numeric (PHP integer-indexed)
  const isNumericKey = function (key) {
    return parseInt(key, 10) + '' === key + ''
  }

  // Helper to check if value is a plain object (not array)
  const isPlainObject = function (val) {
    return val && typeof val === 'object' && toStr.call(val) !== '[object Array]'
  }

  // Process arr1
  for (const key in arr1) {
    if (arr1.hasOwnProperty(key)) {
      if (isNumericKey(key)) {
        result[numericIdx++] = arr1[key]
      } else {
        result[key] = arr1[key]
      }
    }
  }

  // Process arr2
  for (const key in arr2) {
    if (arr2.hasOwnProperty(key)) {
      if (isNumericKey(key)) {
        // Numeric keys always append
        result[numericIdx++] = arr2[key]
      } else if (key in result) {
        // String key exists in both - need to merge
        if (isPlainObject(result[key]) && isPlainObject(arr2[key])) {
          // Both are objects - recurse
          result[key] = array_merge_recursive(result[key], arr2[key])
        } else if (toStr.call(result[key]) === '[object Array]') {
          // Result is already an array, push new value
          result[key].push(arr2[key])
        } else {
          // Create array with both values
          result[key] = [result[key], arr2[key]]
        }
      } else {
        result[key] = arr2[key]
      }
    }
  }

  return result
}

Think you can do better?

Not unlike Wikipedia, Locutus is an ongoing community effort. Our philosophy follows The McDonald’s Theory. This means that we assimilate first iterations with imperfections, hoping for others to take issue with-and improve them. This unorthodox approach has worked very well to foster fun and fruitful collaboration, but please be reminded to use our creations at your own risk. THE SOFTWARE IS PROVIDED "AS IS" has never been more true than for Locutus.

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