feat: Add "mergeAll" and "mergeBy". Update "merge" to allow curried call

src/index.js

@@ -42,7 +42,7 @@ export { isMatch } from "./is-match/is-match"
 // Object
 export { pick } from "./pick/pick"
 export { pluck } from "./pluck/pluck"
-export { merge } from "./merge/merge"
+export { merge, mergeAll, mergeBy } from "./merge/merge"
 export { keys } from "./keys/keys"
 export { zipToObj } from "./zip-to-obj/zip-to-obj"
 

src/merge/merge.js

@@ -1,3 +1,29 @@
+import { is } from "../is/is"
+
+const _merge = (fn, source) => {
+  let result = {}
+
+  for (let i = 0, length = source.length; i < length; i++) {
+    const sourceEntries = Object.entries(source[i])
+
+    if (is(fn)) {
+      result = fn(result, source[i])
+    } else {
+      for (
+        let j = 0, sourceEntriesLength = sourceEntries.length;
+        j < sourceEntriesLength;
+        j++
+      ) {
+        const [key, value] = sourceEntries[j]
+
+        result[key] = value
+      }
+    }
+  }
+
+  return result
+}
+
 /**
  * Combine from left to right, 2 or more objects into a new single one.
  * Properties will be shallow copied. Those with the same name will be
@@ -14,26 +40,24 @@
  * merge({a: "lorem"}, {b: "ipsum", c: 41}, {c: 42, b: undefined})
  * // => { a: "lorem", b: "ipsum", c: 42 }
  */
-const merge = (...sources) => {
-  const result = {}
-
-  for (let i = 0, length = sources.length; i < length; i++) {
-    const sourceEntries = Object.entries(sources[i])
+export const merge = (...params) => {
+  // @signature (obj1) => (obj2)
+  if (params.length <= 1) {
+    return obj2 => _merge(null, [params[0], obj2])
+  }
 
-    for (
-      let j = 0, sourceEntriesLength = sourceEntries.length;
-      j < sourceEntriesLength;
-      j++
-    ) {
-      const [key, value] = sourceEntries[j]
+  // @signature (obj1, obj2)
+  return _merge(null, ...params)
+}
 
-      if (value !== undefined) {
-        result[key] = value
-      }
-    }
+export const mergeBy = (...params) => {
+  // @signature (fn) => (source)
+  if (params.length <= 1) {
+    return source => _merge(params[0], source)
   }
 
-  return result
+  // @signature (fn, source)
+  return _merge(...params)
 }
 
-export { merge }
+export const mergeAll = source => _merge(null, source)

src/merge/merge.test.js

@@ -1,25 +1,34 @@
 import test from "tape"
-import { merge } from ".."
+import { merge, mergeAll, mergeBy } from ".."
 
-test("merge", t => {
+test("merge, mergeAll", t => {
   const obj1 = { a: undefined }
   const obj2 = { a: "lorem", b: "ipsum", c: 41 }
   const obj3 = { c: 42, b: undefined }
-  const result = merge(obj1, obj2, obj3)
 
-  const resultAgain = merge(result, obj1, obj2, obj3)
+  t.deepEqual(
+    mergeBy((a, b) => ({ ...a, ...b }), [obj1, obj2, obj3]),
+    { a: "lorem", b: undefined, c: 42 },
+    "mergeBy 3 objects - uncurried"
+  )
 
   t.deepEqual(
-    result,
-    { a: "lorem", b: "ipsum", c: 42 },
-    "3 objects should be merged into one"
+    mergeBy((a, b) => ({ ...a, ...b }))([obj1, obj2, obj3]),
+    { a: "lorem", b: undefined, c: 42 },
+    "mergeBy 3 objects - curried"
   )
 
-  t.deepEqual(result, resultAgain, "Idempotence")
+  t.deepEqual(
+    mergeAll([obj1, obj2, obj3]),
+    { a: "lorem", b: undefined, c: 42 },
+    "mergeAll 3 objects - uncurried"
+  )
 
-  t.notEqual(result, obj1, "Imutability - first object")
-  t.notEqual(result, obj2, "Imutability - second object")
-  t.notEqual(result, obj3, "Imutability - third object")
+  t.deepEqual(
+    merge(obj1)(obj2),
+    { a: "lorem", b: "ipsum", c: 41 },
+    "merge 2 objects - curried"
+  )
 
   t.end()
 })