[v5] Rewrite shallow to support iterables (#2427)

src/vanilla/shallow.ts

@@ -1,4 +1,22 @@
-export function shallow<T>(objA: T, objB: T) {
+const isIterable = (obj: object): obj is Iterable<unknown> =>
+  Symbol.iterator in obj
+
+const compareMapLike = (
+  iterableA: Iterable<[unknown, unknown]>,
+  iterableB: Iterable<[unknown, unknown]>,
+) => {
+  const mapA = iterableA instanceof Map ? iterableA : new Map(iterableA)
+  const mapB = iterableB instanceof Map ? iterableB : new Map(iterableB)
+  if (mapA.size !== mapB.size) return false
+  for (const [key, value] of mapA) {
+    if (!Object.is(value, mapB.get(key))) {
+      return false
+    }
+  }
+  return true
+}
+
+export function shallow<T>(objA: T, objB: T): boolean {
   if (Object.is(objA, objB)) {
     return true
   }
@@ -11,26 +29,30 @@ export function shallow<T>(objA: T, objB: T) {
     return false
   }
 
-  if (objA instanceof Map && objB instanceof Map) {
-    if (objA.size !== objB.size) return false
-
-    for (const [key, value] of objA) {
-      if (!Object.is(value, objB.get(key))) {
+  if (isIterable(objA) && isIterable(objB)) {
+    const iteratorA = objA[Symbol.iterator]()
+    const iteratorB = objB[Symbol.iterator]()
+    let nextA = iteratorA.next()
+    let nextB = iteratorB.next()
+    if (
+      Array.isArray(nextA.value) &&
+      Array.isArray(nextB.value) &&
+      nextA.value.length === 2 &&
+      nextB.value.length === 2
+    ) {
+      return compareMapLike(
+        objA as Iterable<[unknown, unknown]>,
+        objB as Iterable<[unknown, unknown]>,
+      )
+    }
+    while (!nextA.done && !nextB.done) {
+      if (!Object.is(nextA.value, nextB.value)) {
         return false
       }
+      nextA = iteratorA.next()
+      nextB = iteratorB.next()
     }
-    return true
-  }
-
-  if (objA instanceof Set && objB instanceof Set) {
-    if (objA.size !== objB.size) return false
-
-    for (const value of objA) {
-      if (!objB.has(value)) {
-        return false
-      }
-    }
-    return true
+    return !!nextA.done && !!nextB.done
   }
 
   const keysA = Object.keys(objA)

tests/vanilla/shallow.test.tsx

@@ -91,6 +91,12 @@ describe('shallow', () => {
 
     expect(shallow(firstFnCompare, secondFnCompare)).toBe(false)
   })
+
+  it('compares URLSearchParams', () => {
+    const a = new URLSearchParams({ hello: 'world' })
+    const b = new URLSearchParams({ zustand: 'shallow' })
+    expect(shallow(a, b)).toBe(false)
+  })
 })
 
 describe('unsupported cases', () => {