Merges the enumerable properties of two or more objects deeply. Fastest implementation of deepmerge, see section 'Benchmarks'.
npm i @fastify/deepmerge
The module exports a function, which provides a function to deepmerge Objects.
deepmerge(options)
options is optional and can contain following values
-
symbols(boolean, optional) - should also merge object-keys which are symbols, default is false -
all(boolean, optional) - merges all parameters, 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
const deepmerge = require('@fastify/deepmerge')()
const result = deepmerge({a: 'value'}, { b: 404 })
console.log(result) // {a: 'value', b: 404 }const deepmerge = require('@fastify/deepmerge')({ all: true })
const result = deepmerge({a: 'value'}, { b: 404 }, { a: 404 })
console.log(result) // {a: 404, b: 404 }The default mode to merge Arrays is to concat the source-Array to the target-Array.
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 behaviour regarding merging Arrays, you can provide a function to the
mergeArray 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.
clone: (value: any) => any;
isMergeableObject: (value: any) => any;
deepmerge: DeepMergeFn;
getKeys: (value: object) => string[];The mergeArray-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.
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.
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 behaviour
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 behaviour
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 ] } ]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 prototype (JSON object excluded).
function cloneByReference (source) {
return source
}
const deepmergeByReference = require('@fastify/deepmerge')({
cloneProtoObject: cloneByReference
})
const result = deepmergeByReference({}, { stream: process.stdout })
console.log(result) // { stream: <ref *1> WriteStream }The benchmarks are available in the benchmark-folder.
npm run bench - 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)
npm run bench:compare - 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.