add typedefs from TehShrike#211

src/deepmerge.ts

@@ -1,19 +1,27 @@
-import { getFullOptions } from './options'
+import type { ExplicitOptions, FullOptions, Options } from "./options"
+import { getFullOptions } from "./options"
+import type { DeepMerge, DeepMergeAll, DeepMergeObjects, Property } from "./types"
 import {
 	cloneUnlessOtherwiseSpecified,
 	getKeys,
 	getMergeFunction,
 	propertyIsOnObject,
-	propertyIsUnsafe
-} from './utils'
+	propertyIsUnsafe,
+} from "./utils"
+
+function mergeObject<
+	T1 extends Record<Property, unknown>,
+	T2 extends Record<Property, unknown>,
+	O extends Options
+>(target: T1, source: T2, options: FullOptions<O>): DeepMergeObjects<T1, T2, O> {
+	const destination: any = {}
 
-function mergeObject(target, source, options) {
-	const destination = {}
 	if (options.isMergeable(target)) {
 		getKeys(target).forEach((key) => {
 			destination[key] = cloneUnlessOtherwiseSpecified(target[key], options)
 		})
 	}
+
 	getKeys(source).forEach((key) => {
 		if (propertyIsUnsafe(target, key)) {
 			return
@@ -25,33 +33,73 @@ function mergeObject(target, source, options) {
 			destination[key] = getMergeFunction(key, options)(target[key], source[key], options)
 		}
 	})
+
 	return destination
 }
 
-export function deepmergeImpl(target, source, options) {
+export function deepmergeImpl<T1 extends any, T2 extends any, O extends Options>(
+	target: T1,
+	source: T2,
+	options: FullOptions<O>
+): DeepMerge<T1, T2, ExplicitOptions<O>> {
 	const sourceIsArray = Array.isArray(source)
 	const targetIsArray = Array.isArray(target)
 	const sourceAndTargetTypesMatch = sourceIsArray === targetIsArray
 
 	if (!sourceAndTargetTypesMatch) {
-		return cloneUnlessOtherwiseSpecified(source, options)
+		return cloneUnlessOtherwiseSpecified(source, options) as DeepMerge<T1, T2, ExplicitOptions<O>>
 	} else if (sourceIsArray) {
-		return options.arrayMerge(target, source, options)
+		return options.arrayMerge(target as unknown[], source as unknown[], options) as DeepMerge<
+			T1,
+			T2,
+			ExplicitOptions<O>
+		>
 	} else {
-		return mergeObject(target, source, options)
+		return mergeObject(
+			target as Record<Property, unknown>,
+			source as Record<Property, unknown>,
+			options
+		) as DeepMerge<T1, T2, ExplicitOptions<O>>
 	}
 }
 
-export default function deepmerge(target, source, options) {
+/**
+ * Deeply merge two objects.
+ *
+ * @param target The first object.
+ * @param source The second object.
+ * @param options Deep merge options.
+ */
+export default function deepmerge<
+	T1 extends object,
+	T2 extends object,
+	O extends Options = {}
+>(target: T1, source: T2, options?: O) {
 	return deepmergeImpl(target, source, getFullOptions(options))
 }
 
-export function deepmergeAll(array, options) {
-	if (!Array.isArray(array)) {
-		throw new Error('first argument should be an array')
+/**
+ * Deeply merge two or more objects.
+ *
+ * @param objects An tuple of the objects to merge.
+ * @param options Deep merge options.
+ */
+export function deepmergeAll<
+	Ts extends readonly [object, ...object[]],
+	O extends Options = {}
+>(objects: [...Ts], options?: O): DeepMergeAll<Ts, ExplicitOptions<O>>
+
+/**
+ * Deeply merge two or more objects.
+ *
+ * @param objects An array of the objects to merge.
+ * @param options Deep merge options.
+ */
+export function deepmergeAll(objects: ReadonlyArray<object>, options?: Options): object
+export function deepmergeAll(objects: ReadonlyArray<object>, options?: Options): object {
+	if (!Array.isArray(objects)) {
+		throw new Error(`first argument should be an array`)
 	}
 
-	return array.reduce((prev, next) =>
-		deepmergeImpl(prev, next, getFullOptions(options)), {}
-	)
+	return objects.reduce((prev, next) => deepmergeImpl(prev, next, getFullOptions(options)), {})
 }

src/index.ts

@@ -1 +1,2 @@
 export { default, deepmergeAll } from "./deepmerge"
+export type { Options } from "./options"

src/options.ts

@@ -1,31 +1,89 @@
 import isPlainObj from "is-plain-obj"
 
+import type { Property } from "./types"
 import { cloneUnlessOtherwiseSpecified } from "./utils"
 
-function defaultIsMergeable(value) {
+/**
+ * Deep merge options.
+ */
+export type Options = Partial<{
+	arrayMerge?: ArrayMerge
+	clone?: boolean
+	customMerge?: ObjectMerge
+	isMergeable?: IsMergeable
+}>
+
+/**
+ * Deep merge options with explicit keys.
+ */
+export type ExplicitOptions<O extends Options = Options> = {
+	[K in keyof Options]-?: undefined extends O[K] ? never : O[K]
+}
+
+/**
+ * Deep merge options with defaults applied.
+ */
+export type FullOptions<O extends Options = Options> = {
+	arrayMerge: O["arrayMerge"] extends undefined
+		? typeof defaultArrayMerge
+		: NonNullable<O["arrayMerge"]>
+	clone: O["arrayMerge"] extends undefined ? true : NonNullable<O["clone"]>
+	customMerge?: O["customMerge"]
+	isMergeable: O["arrayMerge"] extends undefined
+		? typeof defaultIsMergeable
+		: NonNullable<O["isMergeable"]>
+	cloneUnlessOtherwiseSpecified: <T>(value: T, options: FullOptions) => T
+}
+
+/**
+ * A function that determins if a type is mergable.
+ */
+export type IsMergeable = (value: any) => boolean
+
+/**
+ * A function that merges any 2 arrays.
+ */
+export type ArrayMerge<T1 = any, T2 = any> = (target: T1[], source: T2[], 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
+
+function defaultIsMergeable(value: unknown): value is Record<Property, unknown> | Array<unknown> {
 	return Array.isArray(value) || isPlainObj(value)
 }
 
-function defaultArrayMerge(target, source, options) {
+function defaultArrayMerge<T1 extends unknown, T2 extends unknown>(
+	target: readonly T1[],
+	source: readonly T2[],
+	options: FullOptions
+) {
 	return [...target, ...source].map((element) =>
 		cloneUnlessOtherwiseSpecified(element, options)
-	)
+	) as T1 extends readonly [...infer E1]
+		? T2 extends readonly [...infer E2]
+			? [...E1, ...E2]
+			: never
+		: never
 }
 
-export function getFullOptions(options) {
+export function getFullOptions<O extends Options>(options?: O) {
 	const overrides =
 		options === undefined
 			? undefined
 			: (Object.fromEntries(
 					// Filter out keys explicitly set to undefined.
 					Object.entries(options).filter(([key, value]) => value !== undefined)
-				))
+			  ) as O)
 
 	return {
 		arrayMerge: defaultArrayMerge,
 		isMergeable: defaultIsMergeable,
 		clone: true,
-	  ...overrides,
-		cloneUnlessOtherwiseSpecified
-	};
+		...overrides,
+		cloneUnlessOtherwiseSpecified,
+	} as FullOptions<O>
 }