diff --git a/lib/web/cache/cache.js b/lib/web/cache/cache.js
index 1f41a66a01b..44f3addafa3 100644
--- a/lib/web/cache/cache.js
+++ b/lib/web/cache/cache.js
@@ -41,7 +41,7 @@ class Cache {
   }
 
   async match (request, options = {}) {
-    webidl.brandCheck(this, Cache)
+    webidl.brandCheck(this, webidl.is.Cache)
 
     const prefix = 'Cache.match'
     webidl.argumentLengthCheck(arguments, 1, prefix)
@@ -59,7 +59,7 @@ class Cache {
   }
 
   async matchAll (request = undefined, options = {}) {
-    webidl.brandCheck(this, Cache)
+    webidl.brandCheck(this, webidl.is.Cache)
 
     const prefix = 'Cache.matchAll'
     if (request !== undefined) request = webidl.converters.RequestInfo(request)
@@ -69,7 +69,7 @@ class Cache {
   }
 
   async add (request) {
-    webidl.brandCheck(this, Cache)
+    webidl.brandCheck(this, webidl.is.Cache)
 
     const prefix = 'Cache.add'
     webidl.argumentLengthCheck(arguments, 1, prefix)
@@ -87,7 +87,7 @@ class Cache {
   }
 
   async addAll (requests) {
-    webidl.brandCheck(this, Cache)
+    webidl.brandCheck(this, webidl.is.Cache)
 
     const prefix = 'Cache.addAll'
     webidl.argumentLengthCheck(arguments, 1, prefix)
@@ -257,7 +257,7 @@ class Cache {
   }
 
   async put (request, response) {
-    webidl.brandCheck(this, Cache)
+    webidl.brandCheck(this, webidl.is.Cache)
 
     const prefix = 'Cache.put'
     webidl.argumentLengthCheck(arguments, 2, prefix)
@@ -388,7 +388,7 @@ class Cache {
   }
 
   async delete (request, options = {}) {
-    webidl.brandCheck(this, Cache)
+    webidl.brandCheck(this, webidl.is.Cache)
 
     const prefix = 'Cache.delete'
     webidl.argumentLengthCheck(arguments, 1, prefix)
@@ -454,7 +454,7 @@ class Cache {
    * @returns {Promise<readonly Request[]>}
    */
   async keys (request = undefined, options = {}) {
-    webidl.brandCheck(this, Cache)
+    webidl.brandCheck(this, webidl.is.Cache)
 
     const prefix = 'Cache.keys'
 
@@ -804,6 +804,12 @@ class Cache {
     // 6.
     return Object.freeze(responseList)
   }
+
+  static {
+    webidl.is.Cache = (arg) => {
+      return arg != null && typeof arg === 'object' && #relevantRequestResponseList in arg
+    }
+  }
 }
 
 Object.defineProperties(Cache.prototype, {
diff --git a/lib/web/cache/cachestorage.js b/lib/web/cache/cachestorage.js
index c49b1e82ec1..8602dc32b6f 100644
--- a/lib/web/cache/cachestorage.js
+++ b/lib/web/cache/cachestorage.js
@@ -21,7 +21,7 @@ class CacheStorage {
   }
 
   async match (request, options = {}) {
-    webidl.brandCheck(this, CacheStorage)
+    webidl.brandCheck(this, webidl.is.CacheStorage)
     webidl.argumentLengthCheck(arguments, 1, 'CacheStorage.match')
 
     request = webidl.converters.RequestInfo(request)
@@ -58,7 +58,7 @@ class CacheStorage {
    * @returns {Promise<boolean>}
    */
   async has (cacheName) {
-    webidl.brandCheck(this, CacheStorage)
+    webidl.brandCheck(this, webidl.is.CacheStorage)
 
     const prefix = 'CacheStorage.has'
     webidl.argumentLengthCheck(arguments, 1, prefix)
@@ -76,7 +76,7 @@ class CacheStorage {
    * @returns {Promise<Cache>}
    */
   async open (cacheName) {
-    webidl.brandCheck(this, CacheStorage)
+    webidl.brandCheck(this, webidl.is.CacheStorage)
 
     const prefix = 'CacheStorage.open'
     webidl.argumentLengthCheck(arguments, 1, prefix)
@@ -110,7 +110,7 @@ class CacheStorage {
    * @returns {Promise<boolean>}
    */
   async delete (cacheName) {
-    webidl.brandCheck(this, CacheStorage)
+    webidl.brandCheck(this, webidl.is.CacheStorage)
 
     const prefix = 'CacheStorage.delete'
     webidl.argumentLengthCheck(arguments, 1, prefix)
@@ -125,7 +125,7 @@ class CacheStorage {
    * @returns {Promise<string[]>}
    */
   async keys () {
-    webidl.brandCheck(this, CacheStorage)
+    webidl.brandCheck(this, webidl.is.CacheStorage)
 
     // 2.1
     const keys = this.#caches.keys()
@@ -133,6 +133,12 @@ class CacheStorage {
     // 2.2
     return [...keys]
   }
+
+  static {
+    webidl.is.CacheStorage = (arg) => {
+      return arg != null && typeof arg === 'object' && #caches in arg
+    }
+  }
 }
 
 Object.defineProperties(CacheStorage.prototype, {
diff --git a/lib/web/cookies/index.js b/lib/web/cookies/index.js
index 8ebff2b1a4c..a612ca86f73 100644
--- a/lib/web/cookies/index.js
+++ b/lib/web/cookies/index.js
@@ -3,9 +3,19 @@
 const { parseSetCookie } = require('./parse')
 const { stringify } = require('./util')
 const { webidl } = require('../webidl')
-const { Headers } = require('../fetch/headers')
 
-const brandChecks = webidl.brandCheckMultiple([Headers, globalThis.Headers].filter(Boolean))
+const globalHeadersBrandCheck = (arg) => webidl.brandCheck(arg, webidl.util.MakeTypeAssertion(globalThis.Headers))
+const undiciHeadersBrandCheck = (arg) => webidl.brandCheck(arg, webidl.is.Headers)
+
+function brandCheckHeaders (arg) {
+  try {
+    undiciHeadersBrandCheck(arg)
+    return
+  } catch {
+  }
+
+  globalHeadersBrandCheck(arg)
+}
 
 /**
  * @typedef {Object} Cookie
@@ -28,7 +38,7 @@ const brandChecks = webidl.brandCheckMultiple([Headers, globalThis.Headers].filt
 function getCookies (headers) {
   webidl.argumentLengthCheck(arguments, 1, 'getCookies')
 
-  brandChecks(headers)
+  brandCheckHeaders(headers)
 
   const cookie = headers.get('cookie')
 
@@ -57,7 +67,7 @@ function getCookies (headers) {
  * @returns {void}
  */
 function deleteCookie (headers, name, attributes) {
-  brandChecks(headers)
+  brandCheckHeaders(headers)
 
   const prefix = 'deleteCookie'
   webidl.argumentLengthCheck(arguments, 2, prefix)
@@ -82,7 +92,7 @@ function deleteCookie (headers, name, attributes) {
 function getSetCookies (headers) {
   webidl.argumentLengthCheck(arguments, 1, 'getSetCookies')
 
-  brandChecks(headers)
+  brandCheckHeaders(headers)
 
   const cookies = headers.getSetCookie()
 
@@ -111,7 +121,7 @@ function parseCookie (cookie) {
 function setCookie (headers, cookie) {
   webidl.argumentLengthCheck(arguments, 2, 'setCookie')
 
-  brandChecks(headers)
+  brandCheckHeaders(headers)
 
   cookie = webidl.converters.Cookie(cookie)
 
diff --git a/lib/web/eventsource/eventsource.js b/lib/web/eventsource/eventsource.js
index 657c0643ca8..93fb1f23436 100644
--- a/lib/web/eventsource/eventsource.js
+++ b/lib/web/eventsource/eventsource.js
@@ -191,6 +191,8 @@ class EventSource extends EventTarget {
    * @readonly
    */
   get readyState () {
+    webidl.brandCheck(this, webidl.is.EventSource)
+
     return this.#readyState
   }
 
@@ -200,6 +202,8 @@ class EventSource extends EventTarget {
    * @returns {string}
    */
   get url () {
+    webidl.brandCheck(this, webidl.is.EventSource)
+
     return this.#url
   }
 
@@ -208,6 +212,8 @@ class EventSource extends EventTarget {
    * instantiated with CORS credentials set (true), or not (false, the default).
    */
   get withCredentials () {
+    webidl.brandCheck(this, webidl.is.EventSource)
+
     return this.#withCredentials
   }
 
@@ -363,7 +369,7 @@ class EventSource extends EventTarget {
    * CLOSED.
    */
   close () {
-    webidl.brandCheck(this, EventSource)
+    webidl.brandCheck(this, webidl.is.EventSource)
 
     if (this.#readyState === CLOSED) return
     this.#readyState = CLOSED
@@ -372,10 +378,14 @@ class EventSource extends EventTarget {
   }
 
   get onopen () {
+    webidl.brandCheck(this, webidl.is.EventSource)
+
     return this.#events.open
   }
 
   set onopen (fn) {
+    webidl.brandCheck(this, webidl.is.EventSource)
+
     if (this.#events.open) {
       this.removeEventListener('open', this.#events.open)
     }
@@ -391,10 +401,14 @@ class EventSource extends EventTarget {
   }
 
   get onmessage () {
+    webidl.brandCheck(this, webidl.is.EventSource)
+
     return this.#events.message
   }
 
   set onmessage (fn) {
+    webidl.brandCheck(this, webidl.is.EventSource)
+
     if (this.#events.message) {
       this.removeEventListener('message', this.#events.message)
     }
@@ -410,10 +424,14 @@ class EventSource extends EventTarget {
   }
 
   get onerror () {
+    webidl.brandCheck(this, webidl.is.EventSource)
+
     return this.#events.error
   }
 
   set onerror (fn) {
+    webidl.brandCheck(this, webidl.is.EventSource)
+
     if (this.#events.error) {
       this.removeEventListener('error', this.#events.error)
     }
@@ -427,6 +445,12 @@ class EventSource extends EventTarget {
       this.#events.error = null
     }
   }
+
+  static {
+    webidl.is.EventSource = (arg) => {
+      return arg != null && typeof arg === 'object' && #events in arg
+    }
+  }
 }
 
 const constantsPropertyDescriptors = {
diff --git a/lib/web/fetch/body.js b/lib/web/fetch/body.js
index a81ddfba437..6209c12d76b 100644
--- a/lib/web/fetch/body.js
+++ b/lib/web/fetch/body.js
@@ -293,7 +293,7 @@ function cloneBody (body) {
   }
 }
 
-function bodyMixinMethods (instance, getInternalState) {
+function bodyMixinMethods (brandCheck, getInternalState) {
   const methods = {
     blob () {
       // The blob() method steps are to return the result of
@@ -313,7 +313,7 @@ function bodyMixinMethods (instance, getInternalState) {
         // Return a Blob whose contents are bytes and type attribute
         // is mimeType.
         return new Blob([bytes], { type: mimeType })
-      }, instance, getInternalState)
+      }, brandCheck, getInternalState)
     },
 
     arrayBuffer () {
@@ -323,19 +323,19 @@ function bodyMixinMethods (instance, getInternalState) {
       // whose contents are bytes.
       return consumeBody(this, (bytes) => {
         return new Uint8Array(bytes).buffer
-      }, instance, getInternalState)
+      }, brandCheck, getInternalState)
     },
 
     text () {
       // The text() method steps are to return the result of running
       // consume body with this and UTF-8 decode.
-      return consumeBody(this, utf8DecodeBytes, instance, getInternalState)
+      return consumeBody(this, utf8DecodeBytes, brandCheck, getInternalState)
     },
 
     json () {
       // The json() method steps are to return the result of running
       // consume body with this and parse JSON from bytes.
-      return consumeBody(this, parseJSONFromBytes, instance, getInternalState)
+      return consumeBody(this, parseJSONFromBytes, brandCheck, getInternalState)
     },
 
     formData () {
@@ -383,7 +383,7 @@ function bodyMixinMethods (instance, getInternalState) {
         throw new TypeError(
           'Content-Type was not one of "multipart/form-data" or "application/x-www-form-urlencoded".'
         )
-      }, instance, getInternalState)
+      }, brandCheck, getInternalState)
     },
 
     bytes () {
@@ -392,7 +392,7 @@ function bodyMixinMethods (instance, getInternalState) {
       // result of creating a Uint8Array from bytes in this’s relevant realm.
       return consumeBody(this, (bytes) => {
         return new Uint8Array(bytes)
-      }, instance, getInternalState)
+      }, brandCheck, getInternalState)
     },
 
     textStream () {
@@ -442,20 +442,20 @@ function bodyMixinMethods (instance, getInternalState) {
   return methods
 }
 
-function mixinBody (prototype, getInternalState) {
-  Object.assign(prototype.prototype, bodyMixinMethods(prototype, getInternalState))
+function mixinBody (prototype, getInternalState, brandCheck) {
+  Object.assign(prototype.prototype, bodyMixinMethods(brandCheck, getInternalState))
 }
 
 /**
  * @see https://fetch.spec.whatwg.org/#concept-body-consume-body
  * @param {any} object internal state
  * @param {(value: unknown) => unknown} convertBytesToJSValue
- * @param {any} instance
+ * @param {import('../../../types/webidl').WebidlIsFunction} brandCheck
  * @param {(target: any) => any} getInternalState
  */
-function consumeBody (object, convertBytesToJSValue, instance, getInternalState) {
+function consumeBody (object, convertBytesToJSValue, brandCheck, getInternalState) {
   try {
-    webidl.brandCheck(object, instance)
+    webidl.brandCheck(object, brandCheck)
   } catch (e) {
     return Promise.reject(e)
   }
diff --git a/lib/web/fetch/formdata.js b/lib/web/fetch/formdata.js
index 226bd329587..e7b8c4c3fb2 100644
--- a/lib/web/fetch/formdata.js
+++ b/lib/web/fetch/formdata.js
@@ -10,6 +10,8 @@ const random = runtimeFeatures.has('crypto')
   ? require('node:crypto').randomInt
   : (max) => Math.floor(Math.random() * max)
 
+let getFormDataState, setFormDataState, getFormDataBoundary
+
 // https://xhr.spec.whatwg.org/#formdata
 class FormData {
   #state = []
@@ -28,7 +30,7 @@ class FormData {
   }
 
   append (name, value, filename = undefined) {
-    webidl.brandCheck(this, FormData)
+    webidl.brandCheck(this, webidl.is.FormData)
 
     const prefix = 'FormData.append'
     webidl.argumentLengthCheck(arguments, 2, prefix)
@@ -56,7 +58,7 @@ class FormData {
   }
 
   delete (name) {
-    webidl.brandCheck(this, FormData)
+    webidl.brandCheck(this, webidl.is.FormData)
 
     const prefix = 'FormData.delete'
     webidl.argumentLengthCheck(arguments, 1, prefix)
@@ -69,7 +71,7 @@ class FormData {
   }
 
   get (name) {
-    webidl.brandCheck(this, FormData)
+    webidl.brandCheck(this, webidl.is.FormData)
 
     const prefix = 'FormData.get'
     webidl.argumentLengthCheck(arguments, 1, prefix)
@@ -89,7 +91,7 @@ class FormData {
   }
 
   getAll (name) {
-    webidl.brandCheck(this, FormData)
+    webidl.brandCheck(this, webidl.is.FormData)
 
     const prefix = 'FormData.getAll'
     webidl.argumentLengthCheck(arguments, 1, prefix)
@@ -106,7 +108,7 @@ class FormData {
   }
 
   has (name) {
-    webidl.brandCheck(this, FormData)
+    webidl.brandCheck(this, webidl.is.FormData)
 
     const prefix = 'FormData.has'
     webidl.argumentLengthCheck(arguments, 1, prefix)
@@ -119,7 +121,7 @@ class FormData {
   }
 
   set (name, value, filename = undefined) {
-    webidl.brandCheck(this, FormData)
+    webidl.brandCheck(this, webidl.is.FormData)
 
     const prefix = 'FormData.set'
     webidl.argumentLengthCheck(arguments, 2, prefix)
@@ -184,40 +186,34 @@ class FormData {
     return `FormData ${output.slice(output.indexOf(']') + 2)}`
   }
 
-  /**
-   * @param {FormData} formData
-   */
-  static getFormDataState (formData) {
-    return formData.#state
-  }
+  static {
+    /** @param {FormData} formData  */
+    getFormDataState = (formData) => formData.#state
 
-  /**
-   * @param {FormData} formData
-   * @param {any[]} newState
-   */
-  static setFormDataState (formData, newState) {
-    formData.#state = newState
-  }
+    /**
+     * @param {FormData} formData
+     * @param {any[]} newState
+     */
+    setFormDataState = (formData, newState) => {
+      formData.#state = newState
+    }
 
-  /**
-   * @param {FormData} formData
-   * @returns {string | null}
-   */
-  static getFormDataBoundary (formData) {
-    const boundary = formData.#boundary
-    if (boundary != null) return boundary
+    /**
+     * @param {FormData} formData
+     * @returns {string | null}
+     */
+    getFormDataBoundary = (formData) => {
+      // eslint-disable-next-line no-return-assign
+      return formData.#boundary ??= `----formdata-undici-0${`${random(1e11)}`.padStart(11, '0')}`
+    }
 
-    // eslint-disable-next-line no-return-assign
-    return formData.#boundary = `----formdata-undici-0${`${random(1e11)}`.padStart(11, '0')}`
+    webidl.is.FormData = (arg) => {
+      return arg != null && typeof arg === 'object' && #state in arg
+    }
   }
 }
 
-const { getFormDataState, setFormDataState, getFormDataBoundary } = FormData
-Reflect.deleteProperty(FormData, 'getFormDataState')
-Reflect.deleteProperty(FormData, 'setFormDataState')
-Reflect.deleteProperty(FormData, 'getFormDataBoundary')
-
-iteratorMixin('FormData', FormData, getFormDataState, 'name', 'value')
+iteratorMixin('FormData', FormData, getFormDataState, 'name', 'value', webidl.is.FormData)
 
 Object.defineProperties(FormData.prototype, {
   append: kEnumerableProperty,
@@ -273,6 +269,4 @@ function makeEntry (name, value, filename) {
   return { name, value }
 }
 
-webidl.is.FormData = webidl.util.MakeTypeAssertion(FormData)
-
 module.exports = { FormData, makeEntry, setFormDataState, getFormDataBoundary }
diff --git a/lib/web/fetch/headers.js b/lib/web/fetch/headers.js
index 024d1989588..8f9fdfb327e 100644
--- a/lib/web/fetch/headers.js
+++ b/lib/web/fetch/headers.js
@@ -423,6 +423,8 @@ class HeadersList {
   }
 }
 
+let getHeadersGuard, setHeadersGuard, getHeadersList, setHeadersList
+
 // https://fetch.spec.whatwg.org/#headers-class
 class Headers {
   #guard
@@ -458,7 +460,7 @@ class Headers {
 
   // https://fetch.spec.whatwg.org/#dom-headers-append
   append (name, value) {
-    webidl.brandCheck(this, Headers)
+    webidl.brandCheck(this, webidl.is.Headers)
 
     webidl.argumentLengthCheck(arguments, 2, 'Headers.append')
 
@@ -471,7 +473,7 @@ class Headers {
 
   // https://fetch.spec.whatwg.org/#dom-headers-delete
   delete (name) {
-    webidl.brandCheck(this, Headers)
+    webidl.brandCheck(this, webidl.is.Headers)
 
     webidl.argumentLengthCheck(arguments, 1, 'Headers.delete')
 
@@ -515,7 +517,7 @@ class Headers {
 
   // https://fetch.spec.whatwg.org/#dom-headers-get
   get (name) {
-    webidl.brandCheck(this, Headers)
+    webidl.brandCheck(this, webidl.is.Headers)
 
     webidl.argumentLengthCheck(arguments, 1, 'Headers.get')
 
@@ -538,7 +540,7 @@ class Headers {
 
   // https://fetch.spec.whatwg.org/#dom-headers-has
   has (name) {
-    webidl.brandCheck(this, Headers)
+    webidl.brandCheck(this, webidl.is.Headers)
 
     webidl.argumentLengthCheck(arguments, 1, 'Headers.has')
 
@@ -561,7 +563,7 @@ class Headers {
 
   // https://fetch.spec.whatwg.org/#dom-headers-set
   set (name, value) {
-    webidl.brandCheck(this, Headers)
+    webidl.brandCheck(this, webidl.is.Headers)
 
     webidl.argumentLengthCheck(arguments, 2, 'Headers.set')
 
@@ -609,7 +611,7 @@ class Headers {
 
   // https://fetch.spec.whatwg.org/#dom-headers-getsetcookie
   getSetCookie () {
-    webidl.brandCheck(this, Headers)
+    webidl.brandCheck(this, webidl.is.Headers)
 
     // 1. If this’s header list does not contain `Set-Cookie`, then return « ».
     // 2. Return the values of all headers in this’s header list whose name is
@@ -630,37 +632,38 @@ class Headers {
     return `Headers ${util.formatWithOptions(options, this.#headersList.entries)}`
   }
 
-  static getHeadersGuard (o) {
-    return o.#guard
-  }
+  static {
+    /** @param {Headers} headers */
+    getHeadersGuard = (headers) => headers.#guard
 
-  static setHeadersGuard (o, guard) {
-    o.#guard = guard
-  }
+    /**
+     * @param {Headers} headers
+     * @param {string} guard
+     */
+    setHeadersGuard = (headers, guard) => {
+      headers.#guard = guard
+    }
 
-  /**
-   * @param {Headers} o
-   */
-  static getHeadersList (o) {
-    return o.#headersList
-  }
+    /**
+     * @param {Headers} headers
+     */
+    getHeadersList = (headers) => headers.#headersList
+
+    /**
+     * @param {Headers} target
+     * @param {HeadersList} list
+     */
+    setHeadersList = (target, list) => {
+      target.#headersList = list
+    }
 
-  /**
-   * @param {Headers} target
-   * @param {HeadersList} list
-   */
-  static setHeadersList (target, list) {
-    target.#headersList = list
+    webidl.is.Headers = (arg) => {
+      return arg != null && typeof arg === 'object' && #guard in arg
+    }
   }
 }
 
-const { getHeadersGuard, setHeadersGuard, getHeadersList, setHeadersList } = Headers
-Reflect.deleteProperty(Headers, 'getHeadersGuard')
-Reflect.deleteProperty(Headers, 'setHeadersGuard')
-Reflect.deleteProperty(Headers, 'getHeadersList')
-Reflect.deleteProperty(Headers, 'setHeadersList')
-
-iteratorMixin('Headers', Headers, headersListSortAndCombine, 0, 1)
+iteratorMixin('Headers', Headers, headersListSortAndCombine, 0, 1, webidl.is.Headers)
 
 Object.defineProperties(Headers.prototype, {
   append: kEnumerableProperty,
diff --git a/lib/web/fetch/request.js b/lib/web/fetch/request.js
index 56945ec02ee..66f8150cb82 100644
--- a/lib/web/fetch/request.js
+++ b/lib/web/fetch/request.js
@@ -83,6 +83,7 @@ function buildAbort (acRef) {
 }
 
 let patchMethodWarning = false
+let setRequestSignal, getRequestDispatcher, setRequestDispatcher, setRequestHeaders, getRequestState, setRequestState, removeRequestAbortListener
 
 // https://fetch.spec.whatwg.org/#request-class
 class Request {
@@ -600,7 +601,7 @@ class Request {
 
   // Returns request’s HTTP method, which is "GET" by default.
   get method () {
-    webidl.brandCheck(this, Request)
+    webidl.brandCheck(this, webidl.is.Request)
 
     // The method getter steps are to return this’s request’s method.
     return this.#state.method
@@ -608,7 +609,7 @@ class Request {
 
   // Returns the URL of request as a string.
   get url () {
-    webidl.brandCheck(this, Request)
+    webidl.brandCheck(this, webidl.is.Request)
 
     // The url getter steps are to return this’s request’s URL, serialized.
     return URLSerializer(this.#state.url)
@@ -618,7 +619,7 @@ class Request {
   // Note that headers added in the network layer by the user agent will not
   // be accounted for in this object, e.g., the "Host" header.
   get headers () {
-    webidl.brandCheck(this, Request)
+    webidl.brandCheck(this, webidl.is.Request)
 
     // The headers getter steps are to return this’s headers.
     return this.#headers
@@ -627,7 +628,7 @@ class Request {
   // Returns the kind of resource requested by request, e.g., "document"
   // or "script".
   get destination () {
-    webidl.brandCheck(this, Request)
+    webidl.brandCheck(this, webidl.is.Request)
 
     // The destination getter are to return this’s request’s destination.
     return this.#state.destination
@@ -639,7 +640,7 @@ class Request {
   // during fetching to determine the value of the `Referer` header of the
   // request being made.
   get referrer () {
-    webidl.brandCheck(this, Request)
+    webidl.brandCheck(this, webidl.is.Request)
 
     // 1. If this’s request’s referrer is "no-referrer", then return the
     // empty string.
@@ -661,7 +662,7 @@ class Request {
   // This is used during fetching to compute the value of the request’s
   // referrer.
   get referrerPolicy () {
-    webidl.brandCheck(this, Request)
+    webidl.brandCheck(this, webidl.is.Request)
 
     // The referrerPolicy getter steps are to return this’s request’s referrer policy.
     return this.#state.referrerPolicy
@@ -671,7 +672,7 @@ class Request {
   // whether the request will use CORS, or will be restricted to same-origin
   // URLs.
   get mode () {
-    webidl.brandCheck(this, Request)
+    webidl.brandCheck(this, webidl.is.Request)
 
     // The mode getter steps are to return this’s request’s mode.
     return this.#state.mode
@@ -681,7 +682,7 @@ class Request {
   // which is a string indicating whether credentials will be sent with the
   // request always, never, or only when sent to a same-origin URL.
   get credentials () {
-    webidl.brandCheck(this, Request)
+    webidl.brandCheck(this, webidl.is.Request)
 
     // The credentials getter steps are to return this’s request’s credentials mode.
     return this.#state.credentials
@@ -691,7 +692,7 @@ class Request {
   // which is a string indicating how the request will
   // interact with the browser’s cache when fetching.
   get cache () {
-    webidl.brandCheck(this, Request)
+    webidl.brandCheck(this, webidl.is.Request)
 
     // The cache getter steps are to return this’s request’s cache mode.
     return this.#state.cache
@@ -702,7 +703,7 @@ class Request {
   // request will be handled during fetching. A request
   // will follow redirects by default.
   get redirect () {
-    webidl.brandCheck(this, Request)
+    webidl.brandCheck(this, webidl.is.Request)
 
     // The redirect getter steps are to return this’s request’s redirect mode.
     return this.#state.redirect
@@ -712,7 +713,7 @@ class Request {
   // cryptographic hash of the resource being fetched. Its value
   // consists of multiple hashes separated by whitespace. [SRI]
   get integrity () {
-    webidl.brandCheck(this, Request)
+    webidl.brandCheck(this, webidl.is.Request)
 
     // The integrity getter steps are to return this’s request’s integrity
     // metadata.
@@ -722,7 +723,7 @@ class Request {
   // Returns a boolean indicating whether or not request can outlive the
   // global in which it was created.
   get keepalive () {
-    webidl.brandCheck(this, Request)
+    webidl.brandCheck(this, webidl.is.Request)
 
     // The keepalive getter steps are to return this’s request’s keepalive.
     return this.#state.keepalive
@@ -731,7 +732,7 @@ class Request {
   // Returns a boolean indicating whether or not request is for a reload
   // navigation.
   get isReloadNavigation () {
-    webidl.brandCheck(this, Request)
+    webidl.brandCheck(this, webidl.is.Request)
 
     // The isReloadNavigation getter steps are to return true if this’s
     // request’s reload-navigation flag is set; otherwise false.
@@ -741,7 +742,7 @@ class Request {
   // Returns a boolean indicating whether or not request is for a history
   // navigation (a.k.a. back-forward navigation).
   get isHistoryNavigation () {
-    webidl.brandCheck(this, Request)
+    webidl.brandCheck(this, webidl.is.Request)
 
     // The isHistoryNavigation getter steps are to return true if this’s request’s
     // history-navigation flag is set; otherwise false.
@@ -752,33 +753,33 @@ class Request {
   // object indicating whether or not request has been aborted, and its
   // abort event handler.
   get signal () {
-    webidl.brandCheck(this, Request)
+    webidl.brandCheck(this, webidl.is.Request)
 
     // The signal getter steps are to return this’s signal.
     return this.#signal
   }
 
   get body () {
-    webidl.brandCheck(this, Request)
+    webidl.brandCheck(this, webidl.is.Request)
 
     return this.#state.body ? this.#state.body.stream : null
   }
 
   get bodyUsed () {
-    webidl.brandCheck(this, Request)
+    webidl.brandCheck(this, webidl.is.Request)
 
     return !!this.#state.body && util.isDisturbed(this.#state.body.stream)
   }
 
   get duplex () {
-    webidl.brandCheck(this, Request)
+    webidl.brandCheck(this, webidl.is.Request)
 
     return 'half'
   }
 
   // Returns a clone of request.
   clone () {
-    webidl.brandCheck(this, Request)
+    webidl.brandCheck(this, webidl.is.Request)
 
     // 1. If this is unusable, then throw a TypeError.
     if (bodyUnusable(this.#state)) {
@@ -840,73 +841,69 @@ class Request {
     return `Request ${nodeUtil.formatWithOptions(options, properties)}`
   }
 
-  /**
-   * @param {Request} request
-   * @param {AbortSignal} newSignal
-   */
-  static setRequestSignal (request, newSignal) {
-    request.#signal = newSignal
-    return request
-  }
+  static {
+    /**
+     * @param {Request} request
+     * @param {AbortSignal} newSignal
+     */
+    setRequestSignal = (request, newSignal) => {
+      request.#signal = newSignal
+    }
 
-  /**
-   * @param {Request} request
-   */
-  static getRequestDispatcher (request) {
-    return request.#dispatcher
-  }
+    /**
+     * @param {Request} request
+     */
+    getRequestDispatcher = (request) => {
+      return request.#dispatcher
+    }
 
-  /**
-   * @param {Request} request
-   * @param {import('../../dispatcher/dispatcher')} newDispatcher
-   */
-  static setRequestDispatcher (request, newDispatcher) {
-    request.#dispatcher = newDispatcher
-  }
+    /**
+     * @param {Request} request
+     * @param {import('../../dispatcher/dispatcher')} newDispatcher
+     */
+    setRequestDispatcher = (request, newDispatcher) => {
+      request.#dispatcher = newDispatcher
+    }
 
-  /**
-   * @param {Request} request
-   * @param {Headers} newHeaders
-   */
-  static setRequestHeaders (request, newHeaders) {
-    request.#headers = newHeaders
-  }
+    /**
+     * @param {Request} request
+     * @param {Headers} newHeaders
+     */
+    setRequestHeaders = (request, newHeaders) => {
+      request.#headers = newHeaders
+    }
 
-  /**
-   * @param {Request} request
-   */
-  static getRequestState (request) {
-    return request.#state
-  }
+    /**
+     * @param {Request} request
+     */
+    getRequestState = (request) => {
+      return request.#state
+    }
 
-  /**
-   * @param {Request} request
-   * @param {any} newState
-   */
-  static setRequestState (request, newState) {
-    request.#state = newState
-  }
+    /**
+     * @param {Request} request
+     * @param {any} newState
+     */
+    setRequestState = (request, newState) => {
+      request.#state = newState
+    }
 
-  /**
-   * Removes the `abort` listener that makes this request's signal follow the
-   * signal passed to its constructor, if any. Idempotent.
-   * @param {Request} request
-   */
-  static removeRequestAbortListener (request) {
-    request.#abortCleanup?.()
+    /**
+     * Removes the `abort` listener that makes this request's signal follow the
+     * signal passed to its constructor, if any. Idempotent.
+     * @param {Request} request
+     */
+    removeRequestAbortListener = (request) => {
+      request.#abortCleanup?.()
+    }
+
+    webidl.is.Request = (arg) => {
+      return arg != null && typeof arg === 'object' && #state in arg
+    }
   }
 }
 
-const { setRequestSignal, getRequestDispatcher, setRequestDispatcher, setRequestHeaders, getRequestState, setRequestState, removeRequestAbortListener } = Request
-Reflect.deleteProperty(Request, 'setRequestSignal')
-Reflect.deleteProperty(Request, 'getRequestDispatcher')
-Reflect.deleteProperty(Request, 'setRequestDispatcher')
-Reflect.deleteProperty(Request, 'setRequestHeaders')
-Reflect.deleteProperty(Request, 'getRequestState')
-Reflect.deleteProperty(Request, 'setRequestState')
-Reflect.deleteProperty(Request, 'removeRequestAbortListener')
-
-mixinBody(Request, getRequestState)
+mixinBody(Request, getRequestState, webidl.is.Request)
 
 // https://fetch.spec.whatwg.org/#requests
 function makeRequest (init) {
@@ -1021,8 +1018,6 @@ Object.defineProperties(Request.prototype, {
   }
 })
 
-webidl.is.Request = webidl.util.MakeTypeAssertion(Request)
-
 /**
  * @param {*} V
  * @returns {import('../../../types/fetch').Request|string}
diff --git a/lib/web/fetch/response.js b/lib/web/fetch/response.js
index f555ea94b15..5e40c164a50 100644
--- a/lib/web/fetch/response.js
+++ b/lib/web/fetch/response.js
@@ -23,6 +23,7 @@ const assert = require('node:assert')
 const { isomorphicEncode, serializeJavascriptValueToJSONString } = require('../infra')
 
 const textEncoder = new TextEncoder('utf-8')
+let getResponseHeaders, setResponseHeaders, getResponseState, setResponseState
 
 // https://fetch.spec.whatwg.org/#response-class
 class Response {
@@ -145,7 +146,7 @@ class Response {
 
   // Returns response’s type, e.g., "cors".
   get type () {
-    webidl.brandCheck(this, Response)
+    webidl.brandCheck(this, webidl.is.Response)
 
     // The type getter steps are to return this’s response’s type.
     return this.#state.type
@@ -153,7 +154,7 @@ class Response {
 
   // Returns response’s URL, if it has one; otherwise the empty string.
   get url () {
-    webidl.brandCheck(this, Response)
+    webidl.brandCheck(this, webidl.is.Response)
 
     const urlList = this.#state.urlList
 
@@ -171,7 +172,7 @@ class Response {
 
   // Returns whether response was obtained through a redirect.
   get redirected () {
-    webidl.brandCheck(this, Response)
+    webidl.brandCheck(this, webidl.is.Response)
 
     // The redirected getter steps are to return true if this’s response’s URL
     // list has more than one item; otherwise false.
@@ -180,7 +181,7 @@ class Response {
 
   // Returns response’s status.
   get status () {
-    webidl.brandCheck(this, Response)
+    webidl.brandCheck(this, webidl.is.Response)
 
     // The status getter steps are to return this’s response’s status.
     return this.#state.status
@@ -188,7 +189,7 @@ class Response {
 
   // Returns whether response’s status is an ok status.
   get ok () {
-    webidl.brandCheck(this, Response)
+    webidl.brandCheck(this, webidl.is.Response)
 
     // The ok getter steps are to return true if this’s response’s status is an
     // ok status; otherwise false.
@@ -197,7 +198,7 @@ class Response {
 
   // Returns response’s status message.
   get statusText () {
-    webidl.brandCheck(this, Response)
+    webidl.brandCheck(this, webidl.is.Response)
 
     // The statusText getter steps are to return this’s response’s status
     // message.
@@ -206,27 +207,27 @@ class Response {
 
   // Returns response’s headers as Headers.
   get headers () {
-    webidl.brandCheck(this, Response)
+    webidl.brandCheck(this, webidl.is.Response)
 
     // The headers getter steps are to return this’s headers.
     return this.#headers
   }
 
   get body () {
-    webidl.brandCheck(this, Response)
+    webidl.brandCheck(this, webidl.is.Response)
 
     return this.#state.body ? this.#state.body.stream : null
   }
 
   get bodyUsed () {
-    webidl.brandCheck(this, Response)
+    webidl.brandCheck(this, webidl.is.Response)
 
     return !!this.#state.body && util.isDisturbed(this.#state.body.stream)
   }
 
   // Returns a clone of response.
   clone () {
-    webidl.brandCheck(this, Response)
+    webidl.brandCheck(this, webidl.is.Response)
 
     // 1. If this is unusable, then throw a TypeError.
     if (bodyUnusable(this.#state)) {
@@ -272,44 +273,44 @@ class Response {
     return `Response ${nodeUtil.formatWithOptions(options, properties)}`
   }
 
-  /**
-   * @param {Response} response
-   */
-  static getResponseHeaders (response) {
-    return response.#headers
-  }
+  static {
+    /**
+     * @param {Response} response
+     */
+    getResponseHeaders = (response) => {
+      return response.#headers
+    }
 
-  /**
-   * @param {Response} response
-   * @param {Headers} newHeaders
-   */
-  static setResponseHeaders (response, newHeaders) {
-    response.#headers = newHeaders
-  }
+    /**
+     * @param {Response} response
+     * @param {Headers} newHeaders
+     */
+    setResponseHeaders = (response, newHeaders) => {
+      response.#headers = newHeaders
+    }
 
-  /**
-   * @param {Response} response
-   */
-  static getResponseState (response) {
-    return response.#state
-  }
+    /**
+     * @param {Response} response
+     */
+    getResponseState = (response) => {
+      return response.#state
+    }
 
-  /**
-   * @param {Response} response
-   * @param {any} newState
-   */
-  static setResponseState (response, newState) {
-    response.#state = newState
+    /**
+     * @param {Response} response
+     * @param {any} newState
+     */
+    setResponseState = (response, newState) => {
+      response.#state = newState
+    }
+
+    webidl.is.Response = (arg) => {
+      return arg != null && typeof arg === 'object' && #state in arg
+    }
   }
 }
 
-const { getResponseHeaders, setResponseHeaders, getResponseState, setResponseState } = Response
-Reflect.deleteProperty(Response, 'getResponseHeaders')
-Reflect.deleteProperty(Response, 'setResponseHeaders')
-Reflect.deleteProperty(Response, 'getResponseState')
-Reflect.deleteProperty(Response, 'setResponseState')
-
-mixinBody(Response, getResponseState)
+mixinBody(Response, getResponseState, webidl.is.Response)
 
 Object.defineProperties(Response.prototype, {
   type: kEnumerableProperty,
@@ -624,8 +625,6 @@ webidl.converters.ResponseInit = webidl.dictionaryConverter([
   }
 ])
 
-webidl.is.Response = webidl.util.MakeTypeAssertion(Response)
-
 module.exports = {
   isNetworkError,
   makeNetworkError,
diff --git a/lib/web/fetch/util.js b/lib/web/fetch/util.js
index 20cbb5c58f6..af6ecfc51b6 100644
--- a/lib/web/fetch/util.js
+++ b/lib/web/fetch/util.js
@@ -872,8 +872,9 @@ function createIterator (name, kInternalIterator, keyIndex = 0, valueIndex = 1)
  * @param {(target: any) => any} kInternalIterator
  * @param {string | number} [keyIndex]
  * @param {string | number} [valueIndex]
+ * @param {import('../../../types/webidl').WebidlIsFunction} brandCheck
  */
-function iteratorMixin (name, object, kInternalIterator, keyIndex = 0, valueIndex = 1) {
+function iteratorMixin (name, object, kInternalIterator, keyIndex = 0, valueIndex = 1, brandCheck) {
   const makeIterator = createIterator(name, kInternalIterator, keyIndex, valueIndex)
 
   const properties = {
@@ -882,7 +883,7 @@ function iteratorMixin (name, object, kInternalIterator, keyIndex = 0, valueInde
       enumerable: true,
       configurable: true,
       value: function keys () {
-        webidl.brandCheck(this, object)
+        webidl.brandCheck(this, brandCheck)
         return makeIterator(this, 'key')
       }
     },
@@ -891,7 +892,7 @@ function iteratorMixin (name, object, kInternalIterator, keyIndex = 0, valueInde
       enumerable: true,
       configurable: true,
       value: function values () {
-        webidl.brandCheck(this, object)
+        webidl.brandCheck(this, brandCheck)
         return makeIterator(this, 'value')
       }
     },
@@ -900,7 +901,7 @@ function iteratorMixin (name, object, kInternalIterator, keyIndex = 0, valueInde
       enumerable: true,
       configurable: true,
       value: function entries () {
-        webidl.brandCheck(this, object)
+        webidl.brandCheck(this, brandCheck)
         return makeIterator(this, 'key+value')
       }
     },
@@ -909,7 +910,7 @@ function iteratorMixin (name, object, kInternalIterator, keyIndex = 0, valueInde
       enumerable: true,
       configurable: true,
       value: function forEach (callbackfn, thisArg = globalThis) {
-        webidl.brandCheck(this, object)
+        webidl.brandCheck(this, brandCheck)
         webidl.argumentLengthCheck(arguments, 1, `${name}.forEach`)
         if (typeof callbackfn !== 'function') {
           throw new TypeError(
diff --git a/lib/web/webidl/index.js b/lib/web/webidl/index.js
index ce81c1e323a..6f4bd5036c0 100644
--- a/lib/web/webidl/index.js
+++ b/lib/web/webidl/index.js
@@ -73,26 +73,14 @@ webidl.errors.invalidArgument = function (context) {
 }
 
 // https://webidl.spec.whatwg.org/#implements
-webidl.brandCheck = function (V, I) {
-  if (!FunctionPrototypeSymbolHasInstance(I, V)) {
+webidl.brandCheck = function (V, is) {
+  if (!is(V)) {
     const err = new TypeError('Illegal invocation')
     err.code = 'ERR_INVALID_THIS' // node compat.
     throw err
   }
 }
 
-webidl.brandCheckMultiple = function (List) {
-  const prototypes = List.map((c) => webidl.util.MakeTypeAssertion(c))
-
-  return (V) => {
-    if (prototypes.every(typeCheck => !typeCheck(V))) {
-      const err = new TypeError('Illegal invocation')
-      err.code = 'ERR_INVALID_THIS' // node compat.
-      throw err
-    }
-  }
-}
-
 webidl.argumentLengthCheck = function ({ length }, min, ctx) {
   if (length < min) {
     throw webidl.errors.exception({
diff --git a/lib/web/websocket/events.js b/lib/web/websocket/events.js
index 7ac9566be46..b31c1d94293 100644
--- a/lib/web/websocket/events.js
+++ b/lib/web/websocket/events.js
@@ -4,6 +4,8 @@ const { webidl } = require('../webidl')
 const { kEnumerableProperty } = require('../../core/util')
 const { kConstruct } = require('../../core/symbols')
 
+let createFastMessageEvent
+
 /**
  * @see https://html.spec.whatwg.org/multipage/comms.html#messageevent
  */
@@ -30,31 +32,31 @@ class MessageEvent extends Event {
   }
 
   get data () {
-    webidl.brandCheck(this, MessageEvent)
+    webidl.brandCheck(this, webidl.is.MessageEvent)
 
     return this.#eventInit.data
   }
 
   get origin () {
-    webidl.brandCheck(this, MessageEvent)
+    webidl.brandCheck(this, webidl.is.MessageEvent)
 
     return this.#eventInit.origin
   }
 
   get lastEventId () {
-    webidl.brandCheck(this, MessageEvent)
+    webidl.brandCheck(this, webidl.is.MessageEvent)
 
     return this.#eventInit.lastEventId
   }
 
   get source () {
-    webidl.brandCheck(this, MessageEvent)
+    webidl.brandCheck(this, webidl.is.MessageEvent)
 
     return this.#eventInit.source
   }
 
   get ports () {
-    webidl.brandCheck(this, MessageEvent)
+    webidl.brandCheck(this, webidl.is.MessageEvent)
 
     if (!Object.isFrozen(this.#eventInit.ports)) {
       Object.freeze(this.#eventInit.ports)
@@ -73,7 +75,7 @@ class MessageEvent extends Event {
     source = null,
     ports = []
   ) {
-    webidl.brandCheck(this, MessageEvent)
+    webidl.brandCheck(this, webidl.is.MessageEvent)
 
     webidl.argumentLengthCheck(arguments, 1, 'MessageEvent.initMessageEvent')
 
@@ -82,21 +84,24 @@ class MessageEvent extends Event {
     })
   }
 
-  static createFastMessageEvent (type, init) {
-    const messageEvent = new MessageEvent(kConstruct, type, init)
-    messageEvent.#eventInit = init
-    messageEvent.#eventInit.data ??= null
-    messageEvent.#eventInit.origin ??= ''
-    messageEvent.#eventInit.lastEventId ??= ''
-    messageEvent.#eventInit.source ??= null
-    messageEvent.#eventInit.ports ??= []
-    return messageEvent
+  static {
+    createFastMessageEvent = (type, init) => {
+      const messageEvent = new MessageEvent(kConstruct, type, init)
+      messageEvent.#eventInit = init
+      messageEvent.#eventInit.data ??= null
+      messageEvent.#eventInit.origin ??= ''
+      messageEvent.#eventInit.lastEventId ??= ''
+      messageEvent.#eventInit.source ??= null
+      messageEvent.#eventInit.ports ??= []
+      return messageEvent
+    }
+
+    webidl.is.MessageEvent = (arg) => {
+      return arg != null && typeof arg === 'object' && #eventInit in arg
+    }
   }
 }
 
-const { createFastMessageEvent } = MessageEvent
-delete MessageEvent.createFastMessageEvent
-
 /**
  * @see https://websockets.spec.whatwg.org/#the-closeevent-interface
  */
@@ -117,22 +122,28 @@ class CloseEvent extends Event {
   }
 
   get wasClean () {
-    webidl.brandCheck(this, CloseEvent)
+    webidl.brandCheck(this, webidl.is.CloseEvent)
 
     return this.#eventInit.wasClean
   }
 
   get code () {
-    webidl.brandCheck(this, CloseEvent)
+    webidl.brandCheck(this, webidl.is.CloseEvent)
 
     return this.#eventInit.code
   }
 
   get reason () {
-    webidl.brandCheck(this, CloseEvent)
+    webidl.brandCheck(this, webidl.is.CloseEvent)
 
     return this.#eventInit.reason
   }
+
+  static {
+    webidl.is.CloseEvent = (arg) => {
+      return arg != null && typeof arg === 'object' && #eventInit in arg
+    }
+  }
 }
 
 // https://html.spec.whatwg.org/multipage/webappapis.html#the-errorevent-interface
@@ -153,34 +164,40 @@ class ErrorEvent extends Event {
   }
 
   get message () {
-    webidl.brandCheck(this, ErrorEvent)
+    webidl.brandCheck(this, webidl.is.ErrorEvent)
 
     return this.#eventInit.message
   }
 
   get filename () {
-    webidl.brandCheck(this, ErrorEvent)
+    webidl.brandCheck(this, webidl.is.ErrorEvent)
 
     return this.#eventInit.filename
   }
 
   get lineno () {
-    webidl.brandCheck(this, ErrorEvent)
+    webidl.brandCheck(this, webidl.is.ErrorEvent)
 
     return this.#eventInit.lineno
   }
 
   get colno () {
-    webidl.brandCheck(this, ErrorEvent)
+    webidl.brandCheck(this, webidl.is.ErrorEvent)
 
     return this.#eventInit.colno
   }
 
   get error () {
-    webidl.brandCheck(this, ErrorEvent)
+    webidl.brandCheck(this, webidl.is.ErrorEvent)
 
     return this.#eventInit.error
   }
+
+  static {
+    webidl.is.ErrorEvent = (arg) => {
+      return arg != null && typeof arg === 'object' && #eventInit in arg
+    }
+  }
 }
 
 Object.defineProperties(MessageEvent.prototype, {
diff --git a/lib/web/websocket/stream/websocketerror.js b/lib/web/websocket/stream/websocketerror.js
index a34c5213a39..04937c271ed 100644
--- a/lib/web/websocket/stream/websocketerror.js
+++ b/lib/web/websocket/stream/websocketerror.js
@@ -26,6 +26,8 @@ function createInheritableDOMException () {
   })
 }
 
+let createUnvalidatedWebSocketError
+
 class WebSocketError extends createInheritableDOMException() {
   #closeCode
   #reason
@@ -77,17 +79,20 @@ class WebSocketError extends createInheritableDOMException() {
    * @param {number|null} code
    * @param {string} reason
    */
-  static createUnvalidatedWebSocketError (message, code, reason) {
-    const error = new WebSocketError(message, kConstruct)
-    error.#closeCode = code
-    error.#reason = reason
-    return error
+  static {
+    createUnvalidatedWebSocketError = (message, code, reason) => {
+      const error = new WebSocketError(message, kConstruct)
+      error.#closeCode = code
+      error.#reason = reason
+      return error
+    }
+
+    webidl.is.WebSocketError = (arg) => {
+      return arg != null && typeof arg === 'object' && #reason in arg
+    }
   }
 }
 
-const { createUnvalidatedWebSocketError } = WebSocketError
-delete WebSocketError.createUnvalidatedWebSocketError
-
 Object.defineProperties(WebSocketError.prototype, {
   closeCode: kEnumerableProperty,
   reason: kEnumerableProperty,
@@ -99,6 +104,4 @@ Object.defineProperties(WebSocketError.prototype, {
   }
 })
 
-webidl.is.WebSocketError = webidl.util.MakeTypeAssertion(WebSocketError)
-
 module.exports = { WebSocketError, createUnvalidatedWebSocketError }
diff --git a/lib/web/websocket/websocket.js b/lib/web/websocket/websocket.js
index 45dbce1bea9..e83343bb4d8 100644
--- a/lib/web/websocket/websocket.js
+++ b/lib/web/websocket/websocket.js
@@ -28,6 +28,8 @@ const { channels } = require('../../core/diagnostics')
 const kRef = Symbol.for('nodejs.ref')
 const kUnref = Symbol.for('nodejs.unref')
 
+let ping
+
 function getSocketAddress (socket) {
   if (typeof socket?.address === 'function') {
     return socket.address()
@@ -198,16 +200,14 @@ class WebSocket extends EventTarget {
     this.#binaryType = 'blob'
   }
 
+  // TODO: remove this
   [kRef] () {
-    webidl.brandCheck(this, WebSocket)
-
     this.#refed = true
     this.#handler.socket?.ref?.()
   }
 
+  // TODO: remove this
   [kUnref] () {
-    webidl.brandCheck(this, WebSocket)
-
     this.#refed = false
     this.#handler.socket?.unref?.()
   }
@@ -218,7 +218,7 @@ class WebSocket extends EventTarget {
    * @param {string|undefined} reason
    */
   close (code = undefined, reason = undefined) {
-    webidl.brandCheck(this, WebSocket)
+    webidl.brandCheck(this, webidl.is.WebSocket)
 
     const prefix = 'WebSocket.close'
 
@@ -245,7 +245,7 @@ class WebSocket extends EventTarget {
    * @param {NodeJS.TypedArray|ArrayBuffer|Blob|string} data
    */
   send (data) {
-    webidl.brandCheck(this, WebSocket)
+    webidl.brandCheck(this, webidl.is.WebSocket)
 
     const prefix = 'WebSocket.send'
     webidl.argumentLengthCheck(arguments, 1, prefix)
@@ -339,45 +339,45 @@ class WebSocket extends EventTarget {
   }
 
   get readyState () {
-    webidl.brandCheck(this, WebSocket)
+    webidl.brandCheck(this, webidl.is.WebSocket)
 
     // The readyState getter steps are to return this's ready state.
     return this.#handler.readyState
   }
 
   get bufferedAmount () {
-    webidl.brandCheck(this, WebSocket)
+    webidl.brandCheck(this, webidl.is.WebSocket)
 
     return this.#bufferedAmount
   }
 
   get url () {
-    webidl.brandCheck(this, WebSocket)
+    webidl.brandCheck(this, webidl.is.WebSocket)
 
     // The url getter steps are to return this's url, serialized.
     return URLSerializer(this.#url)
   }
 
   get extensions () {
-    webidl.brandCheck(this, WebSocket)
+    webidl.brandCheck(this, webidl.is.WebSocket)
 
     return this.#extensions
   }
 
   get protocol () {
-    webidl.brandCheck(this, WebSocket)
+    webidl.brandCheck(this, webidl.is.WebSocket)
 
     return this.#protocol
   }
 
   get onopen () {
-    webidl.brandCheck(this, WebSocket)
+    webidl.brandCheck(this, webidl.is.WebSocket)
 
     return this.#events.open
   }
 
   set onopen (fn) {
-    webidl.brandCheck(this, WebSocket)
+    webidl.brandCheck(this, webidl.is.WebSocket)
 
     if (this.#events.open) {
       this.removeEventListener('open', this.#events.open)
@@ -394,13 +394,13 @@ class WebSocket extends EventTarget {
   }
 
   get onerror () {
-    webidl.brandCheck(this, WebSocket)
+    webidl.brandCheck(this, webidl.is.WebSocket)
 
     return this.#events.error
   }
 
   set onerror (fn) {
-    webidl.brandCheck(this, WebSocket)
+    webidl.brandCheck(this, webidl.is.WebSocket)
 
     if (this.#events.error) {
       this.removeEventListener('error', this.#events.error)
@@ -417,13 +417,13 @@ class WebSocket extends EventTarget {
   }
 
   get onclose () {
-    webidl.brandCheck(this, WebSocket)
+    webidl.brandCheck(this, webidl.is.WebSocket)
 
     return this.#events.close
   }
 
   set onclose (fn) {
-    webidl.brandCheck(this, WebSocket)
+    webidl.brandCheck(this, webidl.is.WebSocket)
 
     if (this.#events.close) {
       this.removeEventListener('close', this.#events.close)
@@ -440,13 +440,13 @@ class WebSocket extends EventTarget {
   }
 
   get onmessage () {
-    webidl.brandCheck(this, WebSocket)
+    webidl.brandCheck(this, webidl.is.WebSocket)
 
     return this.#events.message
   }
 
   set onmessage (fn) {
-    webidl.brandCheck(this, WebSocket)
+    webidl.brandCheck(this, webidl.is.WebSocket)
 
     if (this.#events.message) {
       this.removeEventListener('message', this.#events.message)
@@ -463,13 +463,13 @@ class WebSocket extends EventTarget {
   }
 
   get binaryType () {
-    webidl.brandCheck(this, WebSocket)
+    webidl.brandCheck(this, webidl.is.WebSocket)
 
     return this.#binaryType
   }
 
   set binaryType (type) {
-    webidl.brandCheck(this, WebSocket)
+    webidl.brandCheck(this, webidl.is.WebSocket)
 
     if (type !== 'blob' && type !== 'arraybuffer') {
       this.#binaryType = 'blob'
@@ -654,33 +654,36 @@ class WebSocket extends EventTarget {
     }
   }
 
-  /**
-   * @param {WebSocket} ws
-   * @param {Buffer|undefined} buffer
-   */
-  static ping (ws, buffer) {
-    if (Buffer.isBuffer(buffer)) {
-      if (buffer.length > 125) {
-        throw new TypeError('A PING frame cannot have a body larger than 125 bytes.')
+  static {
+    /**
+     * @param {WebSocket} ws
+     * @param {Buffer|undefined} buffer
+     */
+    ping = (ws, buffer) => {
+      if (Buffer.isBuffer(buffer)) {
+        if (buffer.length > 125) {
+          throw new TypeError('A PING frame cannot have a body larger than 125 bytes.')
+        }
+      } else if (buffer !== undefined) {
+        throw new TypeError('Expected buffer payload')
       }
-    } else if (buffer !== undefined) {
-      throw new TypeError('Expected buffer payload')
-    }
 
-    // An endpoint MAY send a Ping frame any time after the connection is
-    // established and before the connection is closed.
-    const readyState = ws.#handler.readyState
+      // An endpoint MAY send a Ping frame any time after the connection is
+      // established and before the connection is closed.
+      const readyState = ws.#handler.readyState
 
-    if (isEstablished(readyState) && !isClosing(readyState) && !isClosed(readyState)) {
-      const frame = new WebsocketFrameSend(buffer)
-      ws.#handler.socket.write(frame.createFrame(opcodes.PING))
+      if (isEstablished(readyState) && !isClosing(readyState) && !isClosed(readyState)) {
+        const frame = new WebsocketFrameSend(buffer)
+        ws.#handler.socket.write(frame.createFrame(opcodes.PING))
+      }
+    }
+
+    webidl.is.WebSocket = (arg) => {
+      return arg != null && typeof arg === 'object' && #handler in arg
     }
   }
 }
 
-const { ping } = WebSocket
-Reflect.deleteProperty(WebSocket, 'ping')
-
 // https://websockets.spec.whatwg.org/#dom-websocket-connecting
 WebSocket.CONNECTING = WebSocket.prototype.CONNECTING = states.CONNECTING
 // https://websockets.spec.whatwg.org/#dom-websocket-open
diff --git a/types/webidl.d.ts b/types/webidl.d.ts
index b1873b9e52d..6bfe674c9ed 100644
--- a/types/webidl.d.ts
+++ b/types/webidl.d.ts
@@ -248,13 +248,22 @@ type WebidlIsFunction<T> = (arg: any) => arg is T
 interface WebidlIs {
   Request: WebidlIsFunction<undici.Request>
   Response: WebidlIsFunction<undici.Response>
+  Headers: WebidlIsFunction<undici.Headers>
+  FormData: WebidlIsFunction<undici.FormData>
+  WebSocket: WebidlIsFunction<undici.WebSocket>
+  WebSocketError: WebidlIsFunction<undici.WebSocketError>
+  Cache: WebidlIsFunction<undici.Cache>
+  CacheStorage: WebidlIsFunction<undici.CacheStorage>
+  EventSource: WebidlIsFunction<undici.EventSource>
+  MessageEvent: WebidlIsFunction<undici.MessageEvent>
+  CloseEvent: WebidlIsFunction<undici.CloseEvent>
+  ErrorEvent: WebidlIsFunction<undici.ErrorEvent>
+
   ReadableStream: WebidlIsFunction<ReadableStream>
   Blob: WebidlIsFunction<Blob>
   URLSearchParams: WebidlIsFunction<URLSearchParams>
   File: WebidlIsFunction<File>
-  FormData: WebidlIsFunction<undici.FormData>
   URL: WebidlIsFunction<URL>
-  WebSocketError: WebidlIsFunction<undici.WebSocketError>
   AbortSignal: WebidlIsFunction<AbortSignal>
   MessagePort: WebidlIsFunction<MessagePort>
   USVString: WebidlIsFunction<string>
@@ -272,12 +281,9 @@ export interface Webidl {
   attributes: WebIDLExtendedAttributes
 
   /**
-   * @description Performs a brand-check on {@param V} to ensure it is a
-   * {@param cls} object.
+   * @description Performs a brand-check on {@param V}.
    */
-  brandCheck <Interface extends new () => unknown>(V: unknown, cls: Interface): asserts V is Interface
-
-  brandCheckMultiple <Interfaces extends (new () => unknown)[]> (list: Interfaces): (V: any) => asserts V is Interfaces[number]
+  brandCheck <T>(V: unknown, assertion: WebidlIsFunction<T>): asserts V is T
 
   /**
    * @see https://webidl.spec.whatwg.org/#es-sequence