fix: use toString and prototype instead of constructor for type checking

Author: JounQin

.changeset/easy-boxes-shine.md

@@ -0,0 +1,5 @@
+---
+"stable-hash-x": patch
+---
+
+fix: use `toString` and `prototype` instead of `constructor` for type checking

.prettierignore

@@ -1 +1,2 @@
 .yarn
+/public/site.webmanifest

.size-limit.json

@@ -1,6 +1,6 @@
 [
   {
     "path": "./lib/index.js",
-    "limit": "460B"
+    "limit": "540B"
   }
 ]

README.md

@@ -13,7 +13,7 @@
 [![Code Style: Prettier](https://img.shields.io/badge/code_style-prettier-ff69b4.svg)](https://github.com/prettier/prettier)
 [![changesets](https://img.shields.io/badge/maintained%20with-changesets-176de3.svg)](https://github.com/changesets/changesets)
 
-A tiny and fast (460b <sup>[unpkg](https://unpkg.com/stable-hash-x@latest/lib/index.js)</sup>) lib for "stably hashing" a JavaScript value. Originally created for [SWR](https://github.com/vercel/swr) by [Shu Ding][] at [`stable-hash`](https://github.com/shuding/stable-hash), we forked it because the original one is a bit out of maintenance for a long time.
+A tiny and fast (540b <sup>[unpkg](https://unpkg.com/stable-hash-x@latest/lib/index.js)</sup>) lib for "stably hashing" a JavaScript value, works with cross-realm objects. Originally created for [SWR](https://github.com/vercel/swr) by [Shu Ding][] at [`stable-hash`](https://github.com/shuding/stable-hash), we forked it because the original one is a bit out of maintenance for a long time.
 
 It's similar to `JSON.stringify(value)`, but:
 

src/index.ts

@@ -6,6 +6,22 @@ const table = new WeakMap<object, string>()
 // A counter of the key.
 let counter = 0
 
+// eslint-disable-next-line @typescript-eslint/unbound-method
+const { toString } = Object.prototype // type-coverage:ignore-line
+
+const isType = (arg: unknown, type: string): boolean =>
+  toString.call(arg) === `[object ${type}]`
+
+// based on https://github.com/sindresorhus/is-plain-obj
+const isPlainObject = (val: object) => {
+  const prototype: unknown = Object.getPrototypeOf(val)
+  return (
+    prototype === null ||
+    prototype === Object.prototype || // type-coverage:ignore-line
+    Object.getPrototypeOf(prototype) === null
+  )
+}
+
 // A stable hash implementation that supports:
 //  - Fast and ensures unique hash properties
 //  - Handles unserializable values
@@ -17,10 +33,9 @@ let counter = 0
 // eslint-disable-next-line sonarjs/cognitive-complexity
 export function stableHash(arg: unknown): string {
   const type = typeof arg
-  const constructor = arg?.constructor
-  const isDate = constructor === Date
+  const isDate = isType(arg, 'Date')
 
-  if (Object(arg) === arg && !isDate && constructor != RegExp) {
+  if (Object(arg) === arg && !isDate && !isType(arg, 'RegExp')) {
     const arg_ = arg as object
     // Object/function, not null/date/regexp. Use WeakMap to store the id first.
     // If it's already hashed, directly return the result.
@@ -34,15 +49,15 @@ export function stableHash(arg: unknown): string {
     result = ++counter + '~'
     table.set(arg_, result)
     let index: number | string | undefined
-    if (constructor === Array) {
+    if (Array.isArray(arg)) {
       const arg_ = arg as unknown[]
       // Array.
       result = '@'
       for (index = 0; index < arg_.length; index++) {
         result += stableHash(arg_[index]) + ','
       }
       table.set(arg_, result)
-    } else if (constructor === Object) {
+    } else if (isPlainObject(arg_)) {
       // Object, sort keys.
       result = '#'
       // eslint-disable-next-line sonarjs/no-alphabetical-sort
@@ -58,9 +73,11 @@ export function stableHash(arg: unknown): string {
     }
     return result
   }
+
   if (isDate) {
     return (arg as Date).toJSON()
   }
+
   if (type === 'symbol') {
     return (arg as symbol).toString()
   }

tests/unit.spec.ts

@@ -1,5 +1,7 @@
 /* eslint-disable @typescript-eslint/no-empty-function, @typescript-eslint/no-magic-numbers */
 
+import { runInNewContext } from 'node:vm'
+
 import { hash } from 'stable-hash-x'
 
 describe(`Booleans`, () => {
@@ -362,4 +364,21 @@ describe(`The Func-y Bunch featuring The Referential Squad`, () => {
     expect(hash(catMap)).toEqual(hash(catMap))
     expect(hash(catMap)).not.toEqual(hash(catMap2))
   })
+
+  test('across realms', () => {
+    const obj1 = {
+      a: 1,
+      b: new Date('2022-06-25T01:55:27.743Z'),
+      c: /test/,
+      f: Symbol('test'),
+    }
+    const obj2 = runInNewContext(`({
+      a: 1,
+      b: new Date('2022-06-25T01:55:27.743Z'),
+      c: /test/,
+      f: Symbol('test'),
+    })`) as typeof obj1
+    expect(obj1).not.toEqual(obj2)
+    expect(hash(obj1)).toEqual(hash(obj2))
+  })
 })