From 551ae4c87c13f2188b97930eaffd72e5575e9048 Mon Sep 17 00:00:00 2001
From: Daniel Roe <daniel@roe.dev>
Date: Tue, 16 Aug 2022 15:57:19 +0100
Subject: [PATCH] feat: export `Defu` type helper (#45)

---
 README.md    | 11 +++++++++++
 src/defu.ts  |  6 ++++--
 src/types.ts | 22 +++++++++++-----------
 3 files changed, 26 insertions(+), 13 deletions(-)

diff --git a/README.md b/README.md
index f6c2b2f..5010e8a 100644
--- a/README.md
+++ b/README.md
@@ -141,6 +141,17 @@ console.log(defu({ array: ['b', 'c'] }, { array: ['a'] }))
 // => { array: ['a', 'b', 'c']}
 ```
 
+## Type
+
+We expose `Defu` as a type utility to return a merged type that follows the rules that defu follows.
+
+```js
+import type { Defu } from 'defu'
+
+type Options = Defu<{ foo: 'bar' }, [{}, { bar: 'baz' }, { something: 42 }]>
+// returns { foo: 'bar', bar: 'baz', 'something': 42 }
+```
+
 ## License
 
 MIT. Made with 💖
diff --git a/src/defu.ts b/src/defu.ts
index 004e2f7..73d3d9e 100644
--- a/src/defu.ts
+++ b/src/defu.ts
@@ -1,4 +1,4 @@
-import type { Merger, DefuFn, Defu } from './types'
+import type { Merger, DefuFn, DefuInstance } from './types'
 
 function isObject (val: any) {
   return val !== null && typeof val === 'object'
@@ -45,7 +45,7 @@ export function createDefu (merger?: Merger): DefuFn {
 }
 
 // Standard version
-export const defu = createDefu() as Defu
+export const defu = createDefu() as DefuInstance
 export default defu
 
 // Custom version with function merge support
@@ -63,3 +63,5 @@ export const defuArrayFn = createDefu((obj, key, currentValue, _namespace) => {
     return true
   }
 })
+
+export type { Defu } from './types'
diff --git a/src/types.ts b/src/types.ts
index 8666bb9..d370a82 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -1,5 +1,5 @@
-type Input = Record<string | number | symbol, any>
-type IgnoredInput = boolean | number | null | any[] | Record<never, any> | undefined
+export type Input = Record<string | number | symbol, any>
+export type IgnoredInput = boolean | number | null | any[] | Record<never, any> | undefined
 
 export type Merger = <T extends Input, K extends keyof T>(
   obj: T,
@@ -10,7 +10,7 @@ export type Merger = <T extends Input, K extends keyof T>(
 
 type nullish = null | undefined | void
 
-type MergeObjects<
+export type MergeObjects<
   Destination extends Input,
   Defaults extends Input
 > = Destination extends Defaults ? Destination : Omit<Destination, keyof Destination & keyof Defaults> & Omit<Defaults, keyof Destination & keyof Defaults> &
@@ -25,28 +25,28 @@ type MergeObjects<
           : Merge<Destination[Key], Defaults[Key]> // eslint-disable-line no-use-before-define
   }
 
-type Coalesce<S extends Input, D extends Array<Input | IgnoredInput>> =
+export type Defu<S extends Input, D extends Array<Input | IgnoredInput>> =
   D extends [infer F, ...infer Rest]
     ? F extends Input
-      ? Coalesce<MergeObjects<S, F>, Rest>
+      ? Defu<MergeObjects<S, F>, Rest>
       : F extends IgnoredInput
-        ? Coalesce<S, Rest>
+        ? Defu<S, Rest>
         : S
-  : S
+    : S
 
 export type DefuFn = <Source extends Input, Defaults extends Array<Input | IgnoredInput>>(
   source: Source,
   ...defaults: Defaults
-) => Coalesce<Source, Defaults>
+) => Defu<Source, Defaults>
 
-export interface Defu {
-  <Source extends Input, Defaults extends Array<Input | IgnoredInput>>(source: Source | IgnoredInput, ...defaults: Defaults): Coalesce<Source, Defaults>
+export interface DefuInstance {
+  <Source extends Input, Defaults extends Array<Input | IgnoredInput>>(source: Source | IgnoredInput, ...defaults: Defaults): Defu<Source, Defaults>
   fn: DefuFn
   arrayFn: DefuFn
   extend(merger?: Merger): DefuFn
 }
 
-type MergeArrays<Destination, Source> = Destination extends Array<infer DestinationType>
+export type MergeArrays<Destination, Source> = Destination extends Array<infer DestinationType>
   ? Source extends Array<infer SourceType>
     ? Array<DestinationType | SourceType>
     : Source | Array<DestinationType>