Merges the enumerable properties of two or more objects deeply.
npm install @fastify/deepmerge
Merges the enumerable properties of two or more objects deeply. Fastest implementation of deepmerge, see section 'Benchmarks'.
npm i @fastify/deepmerge
$3
The module exports a function, which provides a function to deepmerge Objects.
does not mutate the input objects. It returns a new object, which is the result of the merge.`
deepmerge(options)
is optional and can contain the following values:-
symbols (boolean, optional) - should also merge object keys that are symbols, default is false
- all (boolean, optional) - makes deepmerge accept and merge any number of passed objects, default is false
- mergeArray (function, optional) - provide a function, which returns a function to add custom array merging function
- cloneProtoObject (function, optional) - provide a function, which must return a clone of the object with the prototype of the object
- isMergeableObject (function, optional) - provide a function, which must return true if the object should be merged, default is isMergeableObject from this module
- onlyDefinedProperties (boolean, optional) - if true, properties with undefined in the source will not overwrite existing values from the target, default is falsejs
const deepmerge = require('@fastify/deepmerge')()
const result = deepmerge({a: 'value'}, { b: 404 })
console.log(result) // {a: 'value', b: 404 }
`js
const deepmerge = require('@fastify/deepmerge')({ all: true })
const result = deepmerge({a: 'value'}, { b: 404 }, { a: 404 })
console.log(result) // {a: 404, b: 404 }
`Example with
option:`js
const deepmerge = require('@fastify/deepmerge')({ onlyDefinedProperties: true })
const result = deepmerge({ a: 1, b: null }, { a: undefined, b: undefined })
console.log(result) // { a: 1, b: null }
`#### mergeArray
The default mode to merge Arrays is to concat the source-Array to the target-Array.
js
const target = [1, 2, 3]
const source = [4, 5, 6]
const deepmerge = require('@fastify/deepmerge')()
const result = deepmerge(target, source)
console.log(result) // [1, 2, 3, 4, 5, 6]
`To overwrite the default behavior regarding merging Arrays, you can provide a function to the
option of the deepmerge-function. The function provided to mergeArray
gets an options-parameter passed, which is an Object containing the following keys and values.typescript
clone: (value: any) => any;
isMergeableObject: (value: any) => any;
deepmerge: DeepMergeFn;
getKeys: (value: object) => string[];
`The
-Function needs to return the actual Array merging function, which accepts two parameters of type
Array, and returns a value.Example 1: Replace the target-Array with a clone of the source-Array.
`js
function replaceByClonedSource(options) {
const clone = options.clone
return function (target, source) {
return clone(source)
}
}const deepmerge = require('@fastify/deepmerge')({ mergeArray: replaceByClonedSource })
const result = deepmerge([1, 2, 3], [4, 5, 6])
console.log(result) // [4, 5, 6]
`Example 2: Merge each element of the source-Array with the element at the same index-position of the target-Array.
js
function deepmergeArray(options) {
const deepmerge = options.deepmerge
const clone = options.clone
return function (target, source) {
let i = 0
const tl = target.length
const sl = source.length
const il = Math.max(target.length, source.length)
const result = new Array(il)
for (i = 0; i < il; ++i) {
if (i < sl) {
result[i] = deepmerge(target[i], source[i])
} else {
result[i] = clone(target[i])
}
}
return result
}
}// default behavior
const deepmergeConcatArray = require('@fastify/deepmerge')()
const resultConcatArray = deepmergeConcatArray([{ a: [1, 2, 3 ]}], [{b: [4, 5, 6]}])
console.log(resultConcatArray) // [ { a: [ 1, 2, 3 ]}, { b: [ 4, 5, 6 ] } ]
// modified behavior
const deepmergeDeepmergeArray = require('@fastify/deepmerge')({ mergeArray: deepmergeArray })
const resultDeepmergedArray = deepmergeDeepmergeArray([{ a: [1, 2, 3 ]}], [{b: [4, 5, 6]}])
console.log(resultDeepmergedArray) // [ { a: [ 1, 2, 3 ], b: [ 4, 5, 6 ] } ]
`#### cloneProtoObject
Merging objects with prototypes, such as Streams or Buffers, are not supported by default.
You can provide a custom function to let this module deal with the object that has a
_(JSON object excluded)_.`js
function cloneByReference (source) {
return source
}const deepmergeByReference = require('@fastify/deepmerge')({
cloneProtoObject: cloneByReference
})
const result = deepmergeByReference({}, { stream: process.stdout })
console.log(result) // { stream: WriteStream }
`#### isMergeableObject
By default,
merges all objects except native Date and RegExp objects. To exclude certain objects from being merged, you can provide a custom function to the isMergeableObject option.The default function is exported by this module as
isMergeableObject.The following example shows how to extend the default function to exclude globally defined
FormData objects from being identified as mergeable objects.`js
const { isMergeableObject: defaultIsMergeableObject } = require('@fastify/deepmerge')
function customIsMergeableObject (source) {
return defaultIsMergeableObject(source) && !(source instanceof FormData)
}
const deepmergeWithCustomMergeableObject = require('@fastify/deepmerge')({
isMergeableObject: customIsMergeableObject
})
`Benchmarks
The benchmarks are available in the benchmark folder.
- benchmark various use cases of deepmerge:
`
@fastify/deepmerge: merge regex with date x 1,256,523,040 ops/sec ±0.16% (92 runs sampled)
@fastify/deepmerge: merge object with a primitive x 1,256,082,915 ops/sec ±0.25% (97 runs sampled)
@fastify/deepmerge: merge two arrays containing strings x 25,392,605 ops/sec ±0.22% (97 runs sampled)
@fastify/deepmerge: two merge arrays containing objects x 1,655,426 ops/sec ±0.65% (96 runs sampled)
@fastify/deepmerge: merge two flat objects x 15,571,029 ops/sec ±0.45% (96 runs sampled)
@fastify/deepmerge: merge nested objects x 7,601,328 ops/sec ±0.31% (96 runs sampled)
- comparison of @fastify/deepmerge with other popular deepmerge implementation:
`
@fastify/deepmerge x 605,343 ops/sec ±0.87% (96 runs sampled)
deepmerge x 20,312 ops/sec ±1.06% (92 runs sampled)
merge-deep x 83,167 ops/sec ±1.30% (94 runs sampled)
ts-deepmerge x 175,977 ops/sec ±0.57% (96 runs sampled)
deepmerge-ts x 174,973 ops/sec ±0.44% (93 runs sampled)
lodash.merge x 89,213 ops/sec ±0.70% (98 runs sampled)
Licensed under MIT.