PHP's array_merge_recursive in TypeScript

How to use

Install via yarn add locutus and import: import { array_merge_recursive } from 'locutus/php/array/array_merge_recursive'.

Or with CommonJS: const { array_merge_recursive } = require('locutus/php/array/array_merge_recursive')

Use a bundler that supports tree-shaking so you only ship the functions you actually use. Vite, webpack, Rollup, and Parcel all handle this. For server-side use this is less of a concern.

Examples

These examples are extracted from test cases that automatically verify our functions against their native counterparts.

#	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 TypeScript/JavaScript

Please note that Locutus uses TypeScript/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 TypeScript/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.

In practice most engines preserve insertion order, but if your code depends on key ordering across platforms, keep this caveat in mind.

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

Notes

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

Dependencies

This function uses the following Locutus functions:

• _phpTypes (php/_helpers)

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

TSTypeScript JSJavaScript TSStandalone TS JSStandalone JS

Copy code

import { isObjectLike, type PhpAssoc, type PhpRuntimeValue } from '../_helpers/_phpTypes.ts'

interface MergeObject extends PhpAssoc<MergeValue> {}
type MergeValue = PhpRuntimeValue | MergeValue[] | MergeObject

export function array_merge_recursive(arr1: MergeObject, arr2: MergeObject): MergeObject {
  //       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: MergeObject = {}
  let numericIdx = 0

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

  // Helper to check if value is a plain object (not array)
  const isPlainObject = function (val: PhpRuntimeValue): val is MergeObject {
    return isObjectLike(val) && !Array.isArray(val)
  }

  // Process arr1
  for (const [key, value] of Object.entries(arr1)) {
    if (isNumericKey(key)) {
      result[numericIdx++] = value
    } else {
      result[key] = value
    }
  }

  // Process arr2
  for (const [key, arr2Value] of Object.entries(arr2)) {
    if (isNumericKey(key)) {
      // Numeric keys always append
      result[numericIdx++] = arr2Value
    } else if (key in result) {
      // String key exists in both - need to merge
      const resultValue = result[key]
      if (isPlainObject(resultValue) && isPlainObject(arr2Value)) {
        // Both are objects - recurse
        result[key] = array_merge_recursive(resultValue, arr2Value)
      } else if (Array.isArray(resultValue)) {
        // Result is already an array, push new value
        resultValue.push(arr2Value)
      } else {
        // Create array with both values
        result[key] = [resultValue, arr2Value]
      }
    } else {
      result[key] = arr2Value
    }
  }

  return result
}

import { isObjectLike } from '../_helpers/_phpTypes.ts'

export 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 = {}
  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 isObjectLike(val) && !Array.isArray(val)
  }

  // Process arr1
  for (const [key, value] of Object.entries(arr1)) {
    if (isNumericKey(key)) {
      result[numericIdx++] = value
    } else {
      result[key] = value
    }
  }

  // Process arr2
  for (const [key, arr2Value] of Object.entries(arr2)) {
    if (isNumericKey(key)) {
      // Numeric keys always append
      result[numericIdx++] = arr2Value
    } else if (key in result) {
      // String key exists in both - need to merge
      const resultValue = result[key]
      if (isPlainObject(resultValue) && isPlainObject(arr2Value)) {
        // Both are objects - recurse
        result[key] = array_merge_recursive(resultValue, arr2Value)
      } else if (Array.isArray(resultValue)) {
        // Result is already an array, push new value
        resultValue.push(arr2Value)
      } else {
        // Create array with both values
        result[key] = [resultValue, arr2Value]
      }
    } else {
      result[key] = arr2Value
    }
  }

  return result
}

// php/_helpers/_phpTypes (Locutus helper dependency)
type PhpNullish = null | undefined

type PhpInput = {} | PhpNullish

type PhpScalar = string | number | boolean

type PhpPrimitive = PhpScalar | bigint

type PhpList<T = PhpInput> = T[]

type PhpAssoc<T = PhpInput> = { [key: string]: T }

type PhpArrayLike<T = PhpInput> = PhpList<T> | PhpAssoc<T>

type PhpFunctionValue = (...args: PhpInput[]) => PhpInput

interface PhpRuntimeAssoc {
  [key: string]: PhpRuntimeValue
}

interface PhpRuntimeList extends Array<PhpRuntimeValue> {}

type PhpRuntimeValue = PhpPrimitive | PhpNullish | PhpRuntimeList | PhpRuntimeAssoc | PhpFunctionValue

function isObjectLike(value: PhpInput): value is PhpArrayLike<PhpInput> {
  return typeof value === 'object' && value !== null
}

// php/array/array_merge_recursive (target function module)
interface MergeObject extends PhpAssoc<MergeValue> {}

type MergeValue = PhpRuntimeValue | MergeValue[] | MergeObject

function array_merge_recursive(arr1: MergeObject, arr2: MergeObject): MergeObject {
  //       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: MergeObject = {}
  let numericIdx = 0

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

  // Helper to check if value is a plain object (not array)
  const isPlainObject = function (val: PhpRuntimeValue): val is MergeObject {
    return isObjectLike(val) && !Array.isArray(val)
  }

  // Process arr1
  for (const [key, value] of Object.entries(arr1)) {
    if (isNumericKey(key)) {
      result[numericIdx++] = value
    } else {
      result[key] = value
    }
  }

  // Process arr2
  for (const [key, arr2Value] of Object.entries(arr2)) {
    if (isNumericKey(key)) {
      // Numeric keys always append
      result[numericIdx++] = arr2Value
    } else if (key in result) {
      // String key exists in both - need to merge
      const resultValue = result[key]
      if (isPlainObject(resultValue) && isPlainObject(arr2Value)) {
        // Both are objects - recurse
        result[key] = array_merge_recursive(resultValue, arr2Value)
      } else if (Array.isArray(resultValue)) {
        // Result is already an array, push new value
        resultValue.push(arr2Value)
      } else {
        // Create array with both values
        result[key] = [resultValue, arr2Value]
      }
    } else {
      result[key] = arr2Value
    }
  }

  return result
}

// php/_helpers/_phpTypes (Locutus helper dependency)
function isObjectLike(value) {
  return typeof value === 'object' && value !== null
}

// php/array/array_merge_recursive (target function module)
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 = {}
  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 isObjectLike(val) && !Array.isArray(val)
  }

  // Process arr1
  for (const [key, value] of Object.entries(arr1)) {
    if (isNumericKey(key)) {
      result[numericIdx++] = value
    } else {
      result[key] = value
    }
  }

  // Process arr2
  for (const [key, arr2Value] of Object.entries(arr2)) {
    if (isNumericKey(key)) {
      // Numeric keys always append
      result[numericIdx++] = arr2Value
    } else if (key in result) {
      // String key exists in both - need to merge
      const resultValue = result[key]
      if (isPlainObject(resultValue) && isPlainObject(arr2Value)) {
        // Both are objects - recurse
        result[key] = array_merge_recursive(resultValue, arr2Value)
      } else if (Array.isArray(resultValue)) {
        // Result is already an array, push new value
        resultValue.push(arr2Value)
      } else {
        // Create array with both values
        result[key] = [resultValue, arr2Value]
      }
    } else {
      result[key] = arr2Value
    }
  }

  return result
}

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