feat: don't clone by deafult

re TehShrike#212

changelog.md

@@ -1,5 +1,6 @@
 # [5.0.0](https://github.com/TehShrike/deepmerge/releases/tag/v5.0.0)
 
+- Breaking: Cloning is not turned off by default
 - Breaking: Endpoint are now exported in esm style [#215](https://github.com/TehShrike/deepmerge/pull/215)
   - The main merge function is now a default export
   - The all merge function is now exported as "deepmergeAll" and is no longer a property on the main merge function.

readme.md

@@ -251,11 +251,9 @@ result.pets // => ['Cat', 'Parrot', 'Dog']
 
 #### `clone`
 
-*Deprecated.*
+Defaults to `false`.
 
-Defaults to `true`.
-
-If `clone` is `false` then child objects will be copied directly instead of being cloned.  This was the default behavior before version 2.x.
+If `clone` is `true` then child objects will be cloned into the destination object instead of being directly copied. This was the default behavior before version 5.x.
 
 ## Testing
 

src/options.ts

@@ -8,7 +8,7 @@ import type { FlattenAlias, Property } from "./types"
  */
 export type Options = Partial<{
 	readonly arrayMerge?: ArrayMerge
-	readonly clone?: boolean
+	readonly clone?: Clone
 	readonly customMerge?: ObjectMerge
 	readonly isMergeable?: IsMergeable
 }>
@@ -45,14 +45,19 @@ export type IsMergeable = (value: any) => boolean
  */
 export type ArrayMerge<T1 = any, T2 = any> = (target: Array<T1>, source: Array<T2>, options: FullOptions) => any
 
+/**
+ * The cloning behavior.
+ */
+export type Clone<T = any> = boolean | ((object: T, options: FullOptions) => any)
+
 /**
  * A function that merges any 2 non-arrays values.
  */
 export type ObjectMerge<K = any> = (
 	key: K
 ) => ((target: any, source: any, options: FullOptions) => any) | undefined
 
-const defaultClone = true as const
+const defaultClone = false as const
 
 function defaultIsMergeable(value: unknown): value is Record<Property, unknown> | Array<unknown> {
 	return Array.isArray(value) || isPlainObj(value)

test/merge-all.ts

@@ -61,31 +61,31 @@ test(`invoke merge on every item in array with clone should clone all elements`,
 	t.end()
 })
 
-test(`invoke merge on every item in array clone=false should not clone all elements`, (t) => {
+test(`invoke merge on every item in array clone=true should clone all elements`, (t) => {
 	const firstObject = { a: { d: 123 } }
 	const secondObject = { b: { e: true } }
 	const thirdObject = { c: { f: `string` } }
 
-	const mergedWithoutClone = deepmergeAll([ firstObject, secondObject, thirdObject ], { clone: false })
+	const mergedWithoutClone = deepmergeAll([ firstObject, secondObject, thirdObject ], { clone: true })
 
-	t.equal(mergedWithoutClone.a, firstObject.a)
-	t.equal(mergedWithoutClone.b, secondObject.b)
-	t.equal(mergedWithoutClone.c, thirdObject.c)
+	t.notEqual(mergedWithoutClone.a, firstObject.a)
+	t.notEqual(mergedWithoutClone.b, secondObject.b)
+	t.notEqual(mergedWithoutClone.c, thirdObject.c)
 
 	t.end()
 })
 
 
-test(`invoke merge on every item in array without clone should clone all elements`, (t) => {
+test(`invoke merge on every item in array without clone should not clone all elements`, (t) => {
 	const firstObject = { a: { d: 123 } }
 	const secondObject = { b: { e: true } }
 	const thirdObject = { c: { f: `string` } }
 
 	const mergedWithoutClone = deepmergeAll([ firstObject, secondObject, thirdObject ])
 
-	t.notEqual(mergedWithoutClone.a, firstObject.a)
-	t.notEqual(mergedWithoutClone.b, secondObject.b)
-	t.notEqual(mergedWithoutClone.c, thirdObject.c)
+	t.equal(mergedWithoutClone.a, firstObject.a)
+	t.equal(mergedWithoutClone.b, secondObject.b)
+	t.equal(mergedWithoutClone.c, thirdObject.c)
 
 	t.end()
 })

test/merge-plain-objects.ts

@@ -1,12 +1,12 @@
 import deepmerge from "deepmerge"
 import test from "tape"
 
-test(`plain objects are merged by default`, (t) => {
+test(`plain objects are merged by default and can be cloned`, (t) => {
 	const input = {
 		newObject: new Object(),
 		objectLiteral: { a: 123 },
 	}
-	const output = deepmerge({}, input)
+	const output = deepmerge({}, input, { clone: true })
 
 	t.deepEqual(output.newObject, input.newObject)
 	t.notEqual(output.newObject, input.newObject)
@@ -16,13 +16,13 @@ test(`plain objects are merged by default`, (t) => {
 	t.end()
 })
 
-test(`instantiated objects are copied by reference`, (t) => {
+test(`instantiated objects are copied by reference with clone=true`, (t) => {
 	const input = {
 		date: new Date(),
 		error: new Error(),
 		regex: /regex/,
 	}
-	const output = deepmerge({}, input)
+	const output = deepmerge({}, input, { clone: true })
 
 	t.equal(output.date, input.date)
 	t.equal(output.error, input.error)

test/merge.ts

@@ -139,7 +139,7 @@ test(`should clone source and target`, (t) => {
 	t.end()
 })
 
-test(`should clone source and target`, (t) => {
+test(`should not clone source and target if not told to`, (t) => {
 	const src = {
 		b: {
 			c: `foo`,
@@ -153,8 +153,8 @@ test(`should clone source and target`, (t) => {
 	}
 
 	const merged = deepmerge(target, src)
-	t.notEqual(merged.a, target.a)
-	t.notEqual(merged.b, src.b)
+	t.equal(merged.a, target.a)
+	t.equal(merged.b, src.b)
 
 	t.end()
 })