feat: add defuSchema

README.md

@@ -130,6 +130,19 @@ defuArrayFn({
 
 **Note:** the function is called only if the value defined in defaults is an aray.
 
+## Schema object
+You can use `defuSchema` if you want to remove keys that are not present in the default object.
+
+```js
+console.log(
+  defuSchema(
+      { a: 1, b: 2, c: 3, d: 4 },
+      { a: 2, c: 4, d: 6, e: 8 }
+  )
+);
+// => { a: 1, c: 3, d: 4, e: 8 }
+``
+
 ### Remarks
 
 - `object` and `defaults` are not modified

lib/defu.cjs

@@ -1,4 +1,4 @@
-const { defu, createDefu, defuFn, defuArrayFn } = require('../dist/defu.cjs');
+const { defu, createDefu, defuFn, defuArrayFn, defuSchema } = require('../dist/defu.cjs');
 
 module.exports = defu;
 
@@ -8,4 +8,4 @@ module.exports.default = defu;
 module.exports.createDefu = createDefu;
 module.exports.defuFn = defuFn;
 module.exports.defuArrayFn = defuArrayFn;
-
+module.exports.defuSchema = defuSchema;

src/defu.ts

@@ -1,5 +1,10 @@
 import { isPlainObject } from "./_utils";
-import type { Merger, DefuFn as DefuFunction, DefuInstance } from "./types";
+import type {
+  Merger,
+  DefuFn as DefuFunction,
+  DefuInstance,
+  DefuFnSchema,
+} from "./types";
 
 // Base function to apply defaults
 function _defu<T>(
@@ -73,4 +78,9 @@ export const defuArrayFn = createDefu((object, key, currentValue) => {
   }
 });
 
+// Custom version for skipping keys not present in defaults
+export const defuSchema = createDefu((schema, key) => {
+  return !(key in schema);
+}) as DefuFnSchema;
+
 export type { Defu } from "./types";

src/types.ts

@@ -56,6 +56,24 @@ export type DefuFn = <
   ...defaults: Defaults
 ) => Defu<Source, Defaults>;
 
+export type DefuFnSchema = <
+  Source extends Input,
+  Defaults extends Array<Input | IgnoredInput>,
+>(
+  source: Source,
+  ...defaults: Defaults
+) => Defaults extends [infer F, ...infer Rest]
+  ? F extends Input
+    ? Rest extends Array<Input | IgnoredInput>
+      ? Defu<MergeObjects<F, F>, Rest>
+      : MergeObjects<F, F>
+    : F extends IgnoredInput
+      ? Rest extends Array<Input | IgnoredInput>
+        ? Defu<F, Rest>
+        : F
+      : F
+  : never;
+
 export interface DefuInstance {
   <Source extends Input, Defaults extends Array<Input | IgnoredInput>>(
     source: Source | IgnoredInput,

test/defu.test.ts

@@ -1,6 +1,6 @@
 import { expectTypeOf } from "expect-type";
 import { it, describe, expect } from "vitest";
-import { defu, createDefu, defuFn, defuArrayFn } from "../src/defu";
+import { defu, createDefu, defuFn, defuArrayFn, defuSchema } from "../src/defu";
 import * as asteriskImport from "./fixtures/";
 
 // Part of tests brought from jonschlinkert/defaults-deep (MIT)
@@ -23,6 +23,25 @@ describe("defu", () => {
     expectTypeOf(result2).toMatchTypeOf<{ a: string; d: string }>();
   });
 
+  it("defuSchema(): should skip keys non present in default object", () => {
+    const result = defuSchema(
+      { a: 1, b: 2, c: 3, d: 4 },
+      { a: 2, c: 4, d: 6, e: 8 },
+    );
+    expect(result).toEqual({
+      a: 1,
+      c: 3,
+      d: 4,
+      e: 8,
+    });
+    expectTypeOf(result).toEqualTypeOf<{
+      a: number;
+      c: number;
+      d: number;
+      e: number;
+    }>();
+  });
+
   it("should copy nested values", () => {
     const result = defu({ a: { b: "c" } }, { a: { d: "e" } });
     expect(result).toEqual({