feat: add defu.arrayFn (#21)

README.md

@@ -62,24 +62,59 @@ ext({ cost: 15 }, { cost: 10 }) // { cost: 25 }
 
 ## Function Merger
 
-Using `defu.fn`, if user provided a function, it will be called with default value instead of merging. Mostly useful for array merging.
+Using `defu.fn`, if user provided a function, it will be called with default value instead of merging.
 
-**Example:** Filter some items from defaults (array)
+I can be useful for default values manipulation.
+
+**Example:** Filter some items from defaults (array) and add 20 to the count default value.
 
 ```js
 
 defu.fn({
+  ignore: (val) => val.filter(item => item !== 'dist'),
+  count: (count) => count + 20
+ }, {
+   ignore: ['node_modules','dist],
+   count: 10
+ })
+ /*
+ {
+    ignore: ['node_modules'],
+    count: 30
+  }
+  */
+```
+
+**Note:** if the default value is not defined, the function defined won't be called and kept as value.
+
+## Array Function Merger
+
+`defu.arrayFn` is similar to `defu.fn` but **only applies to array values defined in defaults**.
+
+**Example:** Filter some items from defaults (array) and add 20 to the count default value.
+
+```js
+
+defu.arrayFn({
   ignore(val) => val.filter(i => i !== 'dist'),
-  num: () => 20
+  count: () => 20
  }, {
    ignore: [
      'node_modules',
      'dist
    ],
-   num: 10
- }) // { ignore: ['node_modules'], num: 20 }
+   count: 10
+ })
+ /*
+  {
+    ignore: ['node_modules'],
+    count: () => 20
+  }
+  */
 ```
 
+**Note:** the function is called only if the value defined in defaults is an aray.
+
 ### Remarks
 
 - `object` and `defaults` are not modified
@@ -88,7 +123,7 @@ defu.fn({
 - Will concat `array` values (if default property is defined)
 ```js
 console.log(defu({ array: ['b', 'c'] }, { array: ['a'] }))
-// => { array: [a', 'b', 'c']}
+// => { array: ['a', 'b', 'c']}
 ```
 
 ## License

src/defu.ts

@@ -4,6 +4,7 @@ type DefuFn = <T>(...args: T | any) => T
 interface Defu {
   <T>(...args: T | any): T
   fn: DefuFn
+  arrayFn: DefuFn
   extend(merger?: Merger): DefuFn
 }
 
@@ -55,9 +56,17 @@ function extend (merger?: Merger): DefuFn {
 const defu = extend() as Defu
 
 // Custom version with function merge support
-defu.fn = extend((obj, key, value) => {
-  if (typeof value === 'function') {
-    obj[key] = value(obj[key])
+defu.fn = extend((obj, key, currentValue) => {
+  if (typeof obj[key] !== 'undefined' && typeof currentValue === 'function') {
+    obj[key] = currentValue(obj[key])
+    return true
+  }
+})
+
+// Custom version with function merge support only for defined arrays
+defu.arrayFn = extend((obj, key, currentValue) => {
+  if (Array.isArray(obj[key]) && typeof currentValue === 'function') {
+    obj[key] = currentValue(obj[key])
     return true
   }
 })

test/defu.test.ts

@@ -15,11 +15,15 @@ describe('defu', () => {
   })
 
   it('should copy nested values', () => {
-    expect(defu({ a: { b: 'c' } }, { a: { d: 'e' } })).toEqual({ a: { b: 'c', d: 'e' } })
+    expect(defu({ a: { b: 'c' } }, { a: { d: 'e' } })).toEqual({
+      a: { b: 'c', d: 'e' },
+    })
   })
 
   it('should concat array values by default', () => {
-    expect(defu({ array: ['b', 'c'] }, { array: ['a'] })).toEqual({ array: ['a', 'b', 'c'] })
+    expect(defu({ array: ['b', 'c'] }, { array: ['a'] })).toEqual({
+      array: ['a', 'b', 'c'],
+    })
   })
 
   it('should handle non object first param', () => {
@@ -38,12 +42,14 @@ describe('defu', () => {
     expect(defu({ a: 1 }, { b: 2, a: 'x' }, { c: 3, a: 'x', b: 'x' })).toEqual({
       a: 1,
       b: 2,
-      c: 3
+      c: 3,
     })
   })
 
   it('should not override Object prototype', () => {
-    const payload = JSON.parse('{"constructor": {"prototype": {"isAdmin": true}}}')
+    const payload = JSON.parse(
+      '{"constructor": {"prototype": {"isAdmin": true}}}'
+    )
     defu({}, payload)
     defu(payload, {})
     defu(payload, payload)
@@ -52,7 +58,10 @@ describe('defu', () => {
   })
 
   it('should ignore non-object arguments', () => {
-    expect(defu(null, { foo: 1 }, false, 123, { bar: 2 })).toEqual({ foo: 1, bar: 2 })
+    expect(defu(null, { foo: 1 }, false, 123, { bar: 2 })).toEqual({
+      foo: 1,
+      bar: 2,
+    })
   })
 
   it('custom merger', () => {
@@ -62,28 +71,41 @@ describe('defu', () => {
         return true
       }
     })
-    expect(ext({ cost: 15 }, { cost: 10 }))
-      .toEqual({ cost: 25 })
+    expect(ext({ cost: 15 }, { cost: 10 })).toEqual({ cost: 25 })
   })
 
-  it('custom merger with array', () => {
-    const ext = defu.extend((obj, key, currentValue) => {
-      if (Array.isArray(obj[key]) && typeof currentValue === 'function') {
-        obj[key] = currentValue(obj[key])
-        return true
-      }
-    })
-    expect(ext({ arr: () => ['c'] }, { arr: ['a', 'b'] }))
-      .toEqual({ arr: ['c'] })
+  it('defu.fn()', () => {
     const num = () => 20
-    expect(ext({ num }, { num: 10 }))
-      .toEqual({ num })
+    expect(
+      defu.fn(
+        {
+          ignore: (val) => val.filter((i) => i !== 'dist'),
+          num,
+          ignored: num
+        },
+        {
+          ignore: ['node_modules', 'dist'],
+          num: 10
+        }
+      )
+    ).toEqual({
+      ignore: ['node_modules'],
+      num: 20,
+      ignored: num
+    })
   })
 
-  it('fn merger', () => {
-    expect(defu.fn({ ignore: val => val.filter(i => i !== 'dist') }, { ignore: ['node_modules', 'dist'] }))
-      .toEqual({ ignore: ['node_modules'] })
-    expect(defu.fn({ num: () => 20 }, { num: 10 }))
-      .toEqual({ num: 20 })
+  it('defu.arrayFn()', () => {
+    const num = () => 20
+    expect(defu.arrayFn({
+      arr: () => ['c'],
+      num
+    }, {
+      arr: ['a', 'b'],
+      num: 10
+    })).toEqual({
+      arr: ['c'],
+      num
+    })
   })
 })