diff --git a/lib/fetch/body.js b/lib/fetch/body.js
index 3989b26f620..cf89c7d59f6 100644
--- a/lib/fetch/body.js
+++ b/lib/fetch/body.js
@@ -331,9 +331,7 @@ function bodyMixinMethods (instance) {
     },
 
     async formData () {
-      if (!(this instanceof instance)) {
-        throw new TypeError('Illegal invocation')
-      }
+      webidl.brandCheck(this, instance)
 
       throwIfAborted(this[kState])
 
@@ -435,7 +433,7 @@ function bodyMixinMethods (instance) {
         throwIfAborted(this[kState])
 
         // Otherwise, throw a TypeError.
-        webidl.errors.exception({
+        throw webidl.errors.exception({
           header: `${instance.name}.formData`,
           message: 'Could not parse content as FormData.'
         })
@@ -452,11 +450,8 @@ function mixinBody (prototype) {
 
 // https://fetch.spec.whatwg.org/#concept-body-consume-body
 async function specConsumeBody (object, type, instance) {
-  if (!(object instanceof instance)) {
-    throw new TypeError('Illegal invocation')
-  }
+  webidl.brandCheck(object, instance)
 
-  // TODO: why is this needed?
   throwIfAborted(object[kState])
 
   // 1. If object is unusable, then return a promise rejected
diff --git a/lib/fetch/file.js b/lib/fetch/file.js
index 2cb100de4be..f7a588c9d0f 100644
--- a/lib/fetch/file.js
+++ b/lib/fetch/file.js
@@ -76,25 +76,19 @@ class File extends Blob {
   }
 
   get name () {
-    if (!(this instanceof File)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, File)
 
     return this[kState].name
   }
 
   get lastModified () {
-    if (!(this instanceof File)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, File)
 
     return this[kState].lastModified
   }
 
   get type () {
-    if (!(this instanceof File)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, File)
 
     return this[kState].type
   }
@@ -149,65 +143,49 @@ class FileLike {
   }
 
   stream (...args) {
-    if (!(this instanceof FileLike)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, FileLike)
 
     return this[kState].blobLike.stream(...args)
   }
 
   arrayBuffer (...args) {
-    if (!(this instanceof FileLike)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, FileLike)
 
     return this[kState].blobLike.arrayBuffer(...args)
   }
 
   slice (...args) {
-    if (!(this instanceof FileLike)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, FileLike)
 
     return this[kState].blobLike.slice(...args)
   }
 
   text (...args) {
-    if (!(this instanceof FileLike)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, FileLike)
 
     return this[kState].blobLike.text(...args)
   }
 
   get size () {
-    if (!(this instanceof FileLike)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, FileLike)
 
     return this[kState].blobLike.size
   }
 
   get type () {
-    if (!(this instanceof FileLike)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, FileLike)
 
     return this[kState].blobLike.type
   }
 
   get name () {
-    if (!(this instanceof FileLike)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, FileLike)
 
     return this[kState].name
   }
 
   get lastModified () {
-    if (!(this instanceof FileLike)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, FileLike)
 
     return this[kState].lastModified
   }
diff --git a/lib/fetch/formdata.js b/lib/fetch/formdata.js
index 4b3cc71841a..a2d4ca1a4f5 100644
--- a/lib/fetch/formdata.js
+++ b/lib/fetch/formdata.js
@@ -10,7 +10,7 @@ const { Blob } = require('buffer')
 class FormData {
   constructor (form) {
     if (form !== undefined) {
-      webidl.errors.conversionFailed({
+      throw webidl.errors.conversionFailed({
         prefix: 'FormData constructor',
         argument: 'Argument 1',
         types: ['undefined']
@@ -21,9 +21,7 @@ class FormData {
   }
 
   append (name, value, filename = undefined) {
-    if (!(this instanceof FormData)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, FormData)
 
     if (arguments.length < 2) {
       throw new TypeError(
@@ -56,9 +54,7 @@ class FormData {
   }
 
   delete (name) {
-    if (!(this instanceof FormData)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, FormData)
 
     if (arguments.length < 1) {
       throw new TypeError(
@@ -81,9 +77,7 @@ class FormData {
   }
 
   get (name) {
-    if (!(this instanceof FormData)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, FormData)
 
     if (arguments.length < 1) {
       throw new TypeError(
@@ -106,9 +100,7 @@ class FormData {
   }
 
   getAll (name) {
-    if (!(this instanceof FormData)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, FormData)
 
     if (arguments.length < 1) {
       throw new TypeError(
@@ -128,9 +120,7 @@ class FormData {
   }
 
   has (name) {
-    if (!(this instanceof FormData)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, FormData)
 
     if (arguments.length < 1) {
       throw new TypeError(
@@ -146,9 +136,7 @@ class FormData {
   }
 
   set (name, value, filename = undefined) {
-    if (!(this instanceof FormData)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, FormData)
 
     if (arguments.length < 2) {
       throw new TypeError(
@@ -195,9 +183,7 @@ class FormData {
   }
 
   entries () {
-    if (!(this instanceof FormData)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, FormData)
 
     return makeIterator(
       () => this[kState].map(pair => [pair.name, pair.value]),
@@ -207,9 +193,7 @@ class FormData {
   }
 
   keys () {
-    if (!(this instanceof FormData)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, FormData)
 
     return makeIterator(
       () => this[kState].map(pair => [pair.name, pair.value]),
@@ -219,9 +203,7 @@ class FormData {
   }
 
   values () {
-    if (!(this instanceof FormData)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, FormData)
 
     return makeIterator(
       () => this[kState].map(pair => [pair.name, pair.value]),
@@ -235,9 +217,7 @@ class FormData {
    * @param {unknown} thisArg
    */
   forEach (callbackFn, thisArg = globalThis) {
-    if (!(this instanceof FormData)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, FormData)
 
     if (arguments.length < 1) {
       throw new TypeError(
diff --git a/lib/fetch/headers.js b/lib/fetch/headers.js
index 7ba397032d0..962e8e8f7d0 100644
--- a/lib/fetch/headers.js
+++ b/lib/fetch/headers.js
@@ -38,7 +38,7 @@ function fill (headers, object) {
     for (const header of object) {
       // 1. If header does not contain exactly two items, then throw a TypeError.
       if (header.length !== 2) {
-        webidl.errors.exception({
+        throw webidl.errors.exception({
           header: 'Headers constructor',
           message: `expected name/value pair to be length 2, found ${header.length}.`
         })
@@ -56,7 +56,7 @@ function fill (headers, object) {
       headers.append(key, value)
     }
   } else {
-    webidl.errors.conversionFailed({
+    throw webidl.errors.conversionFailed({
       prefix: 'Headers constructor',
       argument: 'Argument 1',
       types: ['sequence<sequence<ByteString>>', 'record<ByteString, ByteString>']
@@ -173,9 +173,7 @@ class Headers {
 
   // https://fetch.spec.whatwg.org/#dom-headers-append
   append (name, value) {
-    if (!(this instanceof Headers)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, Headers)
 
     if (arguments.length < 2) {
       throw new TypeError(
@@ -192,13 +190,13 @@ class Headers {
     // 2. If name is not a header name or value is not a
     //    header value, then throw a TypeError.
     if (!isValidHeaderName(name)) {
-      webidl.errors.invalidArgument({
+      throw webidl.errors.invalidArgument({
         prefix: 'Headers.append',
         value: name,
         type: 'header name'
       })
     } else if (!isValidHeaderValue(value)) {
-      webidl.errors.invalidArgument({
+      throw webidl.errors.invalidArgument({
         prefix: 'Headers.append',
         value,
         type: 'header value'
@@ -227,9 +225,7 @@ class Headers {
 
   // https://fetch.spec.whatwg.org/#dom-headers-delete
   delete (name) {
-    if (!(this instanceof Headers)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, Headers)
 
     if (arguments.length < 1) {
       throw new TypeError(
@@ -241,7 +237,7 @@ class Headers {
 
     // 1. If name is not a header name, then throw a TypeError.
     if (!isValidHeaderName(name)) {
-      webidl.errors.invalidArgument({
+      throw webidl.errors.invalidArgument({
         prefix: 'Headers.delete',
         value: name,
         type: 'header name'
@@ -278,9 +274,7 @@ class Headers {
 
   // https://fetch.spec.whatwg.org/#dom-headers-get
   get (name) {
-    if (!(this instanceof Headers)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, Headers)
 
     if (arguments.length < 1) {
       throw new TypeError(
@@ -292,7 +286,7 @@ class Headers {
 
     // 1. If name is not a header name, then throw a TypeError.
     if (!isValidHeaderName(name)) {
-      webidl.errors.invalidArgument({
+      throw webidl.errors.invalidArgument({
         prefix: 'Headers.get',
         value: name,
         type: 'header name'
@@ -306,9 +300,7 @@ class Headers {
 
   // https://fetch.spec.whatwg.org/#dom-headers-has
   has (name) {
-    if (!(this instanceof Headers)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, Headers)
 
     if (arguments.length < 1) {
       throw new TypeError(
@@ -320,7 +312,7 @@ class Headers {
 
     // 1. If name is not a header name, then throw a TypeError.
     if (!isValidHeaderName(name)) {
-      webidl.errors.invalidArgument({
+      throw webidl.errors.invalidArgument({
         prefix: 'Headers.has',
         value: name,
         type: 'header name'
@@ -334,9 +326,7 @@ class Headers {
 
   // https://fetch.spec.whatwg.org/#dom-headers-set
   set (name, value) {
-    if (!(this instanceof Headers)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, Headers)
 
     if (arguments.length < 2) {
       throw new TypeError(
@@ -353,13 +343,13 @@ class Headers {
     // 2. If name is not a header name or value is not a
     //    header value, then throw a TypeError.
     if (!isValidHeaderName(name)) {
-      webidl.errors.invalidArgument({
+      throw webidl.errors.invalidArgument({
         prefix: 'Headers.set',
         value: name,
         type: 'header name'
       })
     } else if (!isValidHeaderValue(value)) {
-      webidl.errors.invalidArgument({
+      throw webidl.errors.invalidArgument({
         prefix: 'Headers.set',
         value,
         type: 'header value'
@@ -395,9 +385,7 @@ class Headers {
   }
 
   keys () {
-    if (!(this instanceof Headers)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, Headers)
 
     return makeIterator(
       () => [...this[kHeadersSortedMap].entries()],
@@ -407,9 +395,7 @@ class Headers {
   }
 
   values () {
-    if (!(this instanceof Headers)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, Headers)
 
     return makeIterator(
       () => [...this[kHeadersSortedMap].entries()],
@@ -419,9 +405,7 @@ class Headers {
   }
 
   entries () {
-    if (!(this instanceof Headers)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, Headers)
 
     return makeIterator(
       () => [...this[kHeadersSortedMap].entries()],
@@ -435,9 +419,7 @@ class Headers {
    * @param {unknown} thisArg
    */
   forEach (callbackFn, thisArg = globalThis) {
-    if (!(this instanceof Headers)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, Headers)
 
     if (arguments.length < 1) {
       throw new TypeError(
@@ -457,9 +439,7 @@ class Headers {
   }
 
   [Symbol.for('nodejs.util.inspect.custom')] () {
-    if (!(this instanceof Headers)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, Headers)
 
     return this[kHeadersList]
   }
@@ -493,7 +473,7 @@ webidl.converters.HeadersInit = function (V) {
     return webidl.converters['record<ByteString, ByteString>'](V)
   }
 
-  webidl.errors.conversionFailed({
+  throw webidl.errors.conversionFailed({
     prefix: 'Headers constructor',
     argument: 'Argument 1',
     types: ['sequence<sequence<ByteString>>', 'record<ByteString, ByteString>']
diff --git a/lib/fetch/request.js b/lib/fetch/request.js
index bd4453eba65..40e54d27ab6 100644
--- a/lib/fetch/request.js
+++ b/lib/fetch/request.js
@@ -256,7 +256,7 @@ class Request {
 
     // 17. If mode is "navigate", then throw a TypeError.
     if (mode === 'navigate') {
-      webidl.errors.exception({
+      throw webidl.errors.exception({
         header: 'Request constructor',
         message: 'invalid request mode navigate.'
       })
@@ -500,9 +500,7 @@ class Request {
 
   // Returns request’s HTTP method, which is "GET" by default.
   get method () {
-    if (!(this instanceof Request)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, Request)
 
     // The method getter steps are to return this’s request’s method.
     return this[kState].method
@@ -510,9 +508,7 @@ class Request {
 
   // Returns the URL of request as a string.
   get url () {
-    if (!(this instanceof Request)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, Request)
 
     // The url getter steps are to return this’s request’s URL, serialized.
     return URLSerializer(this[kState].url)
@@ -522,9 +518,7 @@ 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 () {
-    if (!(this instanceof Request)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, Request)
 
     // The headers getter steps are to return this’s headers.
     return this[kHeaders]
@@ -533,9 +527,7 @@ class Request {
   // Returns the kind of resource requested by request, e.g., "document"
   // or "script".
   get destination () {
-    if (!(this instanceof Request)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, Request)
 
     // The destination getter are to return this’s request’s destination.
     return this[kState].destination
@@ -547,9 +539,7 @@ class Request {
   // during fetching to determine the value of the `Referer` header of the
   // request being made.
   get referrer () {
-    if (!(this instanceof Request)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, Request)
 
     // 1. If this’s request’s referrer is "no-referrer", then return the
     // empty string.
@@ -571,9 +561,7 @@ class Request {
   // This is used during fetching to compute the value of the request’s
   // referrer.
   get referrerPolicy () {
-    if (!(this instanceof Request)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, Request)
 
     // The referrerPolicy getter steps are to return this’s request’s referrer policy.
     return this[kState].referrerPolicy
@@ -583,9 +571,7 @@ class Request {
   // whether the request will use CORS, or will be restricted to same-origin
   // URLs.
   get mode () {
-    if (!(this instanceof Request)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, Request)
 
     // The mode getter steps are to return this’s request’s mode.
     return this[kState].mode
@@ -603,9 +589,7 @@ class Request {
   // which is a string indicating how the request will
   // interact with the browser’s cache when fetching.
   get cache () {
-    if (!(this instanceof Request)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, Request)
 
     // The cache getter steps are to return this’s request’s cache mode.
     return this[kState].cache
@@ -616,9 +600,7 @@ class Request {
   // request will be handled during fetching. A request
   // will follow redirects by default.
   get redirect () {
-    if (!(this instanceof Request)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, Request)
 
     // The redirect getter steps are to return this’s request’s redirect mode.
     return this[kState].redirect
@@ -628,9 +610,7 @@ class Request {
   // cryptographic hash of the resource being fetched. Its value
   // consists of multiple hashes separated by whitespace. [SRI]
   get integrity () {
-    if (!(this instanceof Request)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, Request)
 
     // The integrity getter steps are to return this’s request’s integrity
     // metadata.
@@ -640,9 +620,7 @@ class Request {
   // Returns a boolean indicating whether or not request can outlive the
   // global in which it was created.
   get keepalive () {
-    if (!(this instanceof Request)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, Request)
 
     // The keepalive getter steps are to return this’s request’s keepalive.
     return this[kState].keepalive
@@ -651,9 +629,7 @@ class Request {
   // Returns a boolean indicating whether or not request is for a reload
   // navigation.
   get isReloadNavigation () {
-    if (!(this instanceof Request)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, Request)
 
     // The isReloadNavigation getter steps are to return true if this’s
     // request’s reload-navigation flag is set; otherwise false.
@@ -663,9 +639,7 @@ class Request {
   // Returns a boolean indicating whether or not request is for a history
   // navigation (a.k.a. back-foward navigation).
   get isHistoryNavigation () {
-    if (!(this instanceof Request)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, Request)
 
     // The isHistoryNavigation getter steps are to return true if this’s request’s
     // history-navigation flag is set; otherwise false.
@@ -676,43 +650,33 @@ class Request {
   // object indicating whether or not request has been aborted, and its
   // abort event handler.
   get signal () {
-    if (!(this instanceof Request)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, Request)
 
     // The signal getter steps are to return this’s signal.
     return this[kSignal]
   }
 
   get body () {
-    if (!this || !this[kState]) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, Request)
 
     return this[kState].body ? this[kState].body.stream : null
   }
 
   get bodyUsed () {
-    if (!this || !this[kState]) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, Request)
 
     return !!this[kState].body && util.isDisturbed(this[kState].body.stream)
   }
 
   get duplex () {
-    if (!(this instanceof Request)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, Request)
 
     return 'half'
   }
 
   // Returns a clone of request.
   clone () {
-    if (!(this instanceof Request)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, Request)
 
     // 1. If this is unusable, then throw a TypeError.
     if (this.bodyUsed || this.body?.locked) {
diff --git a/lib/fetch/response.js b/lib/fetch/response.js
index 6ef9aa1c423..d3151d88d40 100644
--- a/lib/fetch/response.js
+++ b/lib/fetch/response.js
@@ -171,9 +171,7 @@ class Response {
 
   // Returns response’s type, e.g., "cors".
   get type () {
-    if (!(this instanceof Response)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, Response)
 
     // The type getter steps are to return this’s response’s type.
     return this[kState].type
@@ -181,9 +179,7 @@ class Response {
 
   // Returns response’s URL, if it has one; otherwise the empty string.
   get url () {
-    if (!(this instanceof Response)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, Response)
 
     const urlList = this[kState].urlList
 
@@ -201,9 +197,7 @@ class Response {
 
   // Returns whether response was obtained through a redirect.
   get redirected () {
-    if (!(this instanceof Response)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, Response)
 
     // The redirected getter steps are to return true if this’s response’s URL
     // list has more than one item; otherwise false.
@@ -212,9 +206,7 @@ class Response {
 
   // Returns response’s status.
   get status () {
-    if (!(this instanceof Response)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, Response)
 
     // The status getter steps are to return this’s response’s status.
     return this[kState].status
@@ -222,9 +214,7 @@ class Response {
 
   // Returns whether response’s status is an ok status.
   get ok () {
-    if (!(this instanceof Response)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, Response)
 
     // The ok getter steps are to return true if this’s response’s status is an
     // ok status; otherwise false.
@@ -233,9 +223,7 @@ class Response {
 
   // Returns response’s status message.
   get statusText () {
-    if (!(this instanceof Response)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, Response)
 
     // The statusText getter steps are to return this’s response’s status
     // message.
@@ -244,39 +232,31 @@ class Response {
 
   // Returns response’s headers as Headers.
   get headers () {
-    if (!(this instanceof Response)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, Response)
 
     // The headers getter steps are to return this’s headers.
     return this[kHeaders]
   }
 
   get body () {
-    if (!this || !this[kState]) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, Response)
 
     return this[kState].body ? this[kState].body.stream : null
   }
 
   get bodyUsed () {
-    if (!this || !this[kState]) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, Response)
 
     return !!this[kState].body && util.isDisturbed(this[kState].body.stream)
   }
 
   // Returns a clone of response.
   clone () {
-    if (!(this instanceof Response)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, Response)
 
     // 1. If this is unusable, then throw a TypeError.
     if (this.bodyUsed || (this.body && this.body.locked)) {
-      webidl.errors.exception({
+      throw webidl.errors.exception({
         header: 'Response.clone',
         message: 'Body has already been consumed.'
       })
@@ -504,7 +484,7 @@ function initializeResponse (response, init, body) {
   if (body) {
     // 1. If response's status is a null body status, then throw a TypeError.
     if (nullBodyStatus.includes(response.status)) {
-      webidl.errors.exception({
+      throw webidl.errors.exception({
         header: 'Response constructor',
         message: 'Invalid response status code.'
       })
diff --git a/lib/fetch/webidl.js b/lib/fetch/webidl.js
index cd42de2ac8a..31dcb1ddfa6 100644
--- a/lib/fetch/webidl.js
+++ b/lib/fetch/webidl.js
@@ -3,30 +3,16 @@
 const { types } = require('util')
 const { hasOwn, toUSVString } = require('./util')
 
+/** @type {import('../../types/webidl').Webidl} */
 const webidl = {}
 webidl.converters = {}
 webidl.util = {}
 webidl.errors = {}
 
-/**
- *
- * @param {{
- *   header: string
- *   message: string
- * }} message
- */
 webidl.errors.exception = function (message) {
-  throw new TypeError(`${message.header}: ${message.message}`)
+  return new TypeError(`${message.header}: ${message.message}`)
 }
 
-/**
- * Throw an error when conversion from one type to another has failed
- * @param {{
- *   prefix: string
- *   argument: string
- *   types: string[]
- * }} context
- */
 webidl.errors.conversionFailed = function (context) {
   const plural = context.types.length === 1 ? '' : ' one of'
   const message =
@@ -39,14 +25,6 @@ webidl.errors.conversionFailed = function (context) {
   })
 }
 
-/**
- * Throw an error when an invalid argument is provided
- * @param {{
- *   prefix: string
- *   value: string
- *   type: string
- * }} context
- */
 webidl.errors.invalidArgument = function (context) {
   return webidl.errors.exception({
     header: context.prefix,
@@ -54,6 +32,13 @@ webidl.errors.invalidArgument = function (context) {
   })
 }
 
+// https://webidl.spec.whatwg.org/#implements
+webidl.brandCheck = function (V, I) {
+  if (!(V instanceof I)) {
+    throw new TypeError('Illegal invocation')
+  }
+}
+
 // https://tc39.es/ecma262/#sec-ecmascript-data-types-and-values
 webidl.util.Type = function (V) {
   switch (typeof V) {
@@ -126,7 +111,7 @@ webidl.util.ConvertToInt = function (V, bitLength, signedness, opts = {}) {
       x === Number.POSITIVE_INFINITY ||
       x === Number.NEGATIVE_INFINITY
     ) {
-      webidl.errors.exception({
+      throw webidl.errors.exception({
         header: 'Integer conversion',
         message: `Could not convert ${V} to an integer.`
       })
@@ -138,7 +123,7 @@ webidl.util.ConvertToInt = function (V, bitLength, signedness, opts = {}) {
     // 3. If x < lowerBound or x > upperBound, then
     //    throw a TypeError.
     if (x < lowerBound || x > upperBound) {
-      webidl.errors.exception({
+      throw webidl.errors.exception({
         header: 'Integer conversion',
         message: `Value must be between ${lowerBound}-${upperBound}, got ${x}.`
       })
@@ -213,7 +198,7 @@ webidl.sequenceConverter = function (converter) {
   return (V) => {
     // 1. If Type(V) is not Object, throw a TypeError.
     if (webidl.util.Type(V) !== 'Object') {
-      webidl.errors.exception({
+      throw webidl.errors.exception({
         header: 'Sequence',
         message: `Value of type ${webidl.util.Type(V)} is not an Object.`
       })
@@ -229,7 +214,7 @@ webidl.sequenceConverter = function (converter) {
       method === undefined ||
       typeof method.next !== 'function'
     ) {
-      webidl.errors.exception({
+      throw webidl.errors.exception({
         header: 'Sequence',
         message: 'Object is not an iterator.'
       })
@@ -255,7 +240,7 @@ webidl.recordConverter = function (keyConverter, valueConverter) {
   return (O) => {
     // 1. If Type(O) is not Object, throw a TypeError.
     if (webidl.util.Type(O) !== 'Object') {
-      webidl.errors.exception({
+      throw webidl.errors.exception({
         header: 'Record',
         message: `Value of type ${webidl.util.Type(O)} is not an Object.`
       })
@@ -314,7 +299,7 @@ webidl.recordConverter = function (keyConverter, valueConverter) {
 webidl.interfaceConverter = function (i) {
   return (V, opts = {}) => {
     if (opts.strict !== false && !(V instanceof i)) {
-      webidl.errors.exception({
+      throw webidl.errors.exception({
         header: i.name,
         message: `Expected ${V} to be an instance of ${i.name}.`
       })
@@ -324,16 +309,6 @@ webidl.interfaceConverter = function (i) {
   }
 }
 
-/**
- * @param {{
- *   key: string,
- *   defaultValue?: any,
- *   required?: boolean,
- *   converter: (...args: unknown[]) => unknown,
- *   allowedValues?: any[]
- * }[]} converters
- * @returns
- */
 webidl.dictionaryConverter = function (converters) {
   return (dictionary) => {
     const type = webidl.util.Type(dictionary)
@@ -342,7 +317,7 @@ webidl.dictionaryConverter = function (converters) {
     if (type === 'Null' || type === 'Undefined') {
       return dict
     } else if (type !== 'Object') {
-      webidl.errors.exception({
+      throw webidl.errors.exception({
         header: 'Dictionary',
         message: `Expected ${dictionary} to be one of: Null, Undefined, Object.`
       })
@@ -353,7 +328,7 @@ webidl.dictionaryConverter = function (converters) {
 
       if (required === true) {
         if (!hasOwn(dictionary, key)) {
-          webidl.errors.exception({
+          throw webidl.errors.exception({
             header: 'Dictionary',
             message: `Missing required key "${key}".`
           })
@@ -379,7 +354,7 @@ webidl.dictionaryConverter = function (converters) {
           options.allowedValues &&
           !options.allowedValues.includes(value)
         ) {
-          webidl.errors.exception({
+          throw webidl.errors.exception({
             header: 'Dictionary',
             message: `${value} is not an accepted type. Expected one of ${options.allowedValues.join(', ')}.`
           })
@@ -450,7 +425,6 @@ webidl.converters.ByteString = function (V) {
 }
 
 // https://webidl.spec.whatwg.org/#es-USVString
-// TODO: ensure that util.toUSVString follows webidl spec
 webidl.converters.USVString = toUSVString
 
 // https://webidl.spec.whatwg.org/#es-boolean
@@ -469,9 +443,9 @@ webidl.converters.any = function (V) {
 }
 
 // https://webidl.spec.whatwg.org/#es-long-long
-webidl.converters['long long'] = function (V, opts) {
+webidl.converters['long long'] = function (V) {
   // 1. Let x be ? ConvertToInt(V, 64, "signed").
-  const x = webidl.util.ConvertToInt(V, 64, 'signed', opts)
+  const x = webidl.util.ConvertToInt(V, 64, 'signed')
 
   // 2. Return the IDL long long value that represents
   //    the same numeric value as x.
@@ -509,7 +483,7 @@ webidl.converters.ArrayBuffer = function (V, opts = {}) {
     webidl.util.Type(V) !== 'Object' ||
     !types.isAnyArrayBuffer(V)
   ) {
-    webidl.errors.conversionFailed({
+    throw webidl.errors.conversionFailed({
       prefix: `${V}`,
       argument: `${V}`,
       types: ['ArrayBuffer']
@@ -521,7 +495,7 @@ webidl.converters.ArrayBuffer = function (V, opts = {}) {
   //    IsSharedArrayBuffer(V) is true, then throw a
   //    TypeError.
   if (opts.allowShared === false && types.isSharedArrayBuffer(V)) {
-    webidl.errors.exception({
+    throw webidl.errors.exception({
       header: 'ArrayBuffer',
       message: 'SharedArrayBuffer is not allowed.'
     })
@@ -549,7 +523,7 @@ webidl.converters.TypedArray = function (V, T, opts = {}) {
     !types.isTypedArray(V) ||
     V.constructor.name !== T.name
   ) {
-    webidl.errors.conversionFailed({
+    throw webidl.errors.conversionFailed({
       prefix: `${T.name}`,
       argument: `${V}`,
       types: [T.name]
@@ -561,7 +535,7 @@ webidl.converters.TypedArray = function (V, T, opts = {}) {
   //    IsSharedArrayBuffer(V.[[ViewedArrayBuffer]]) is
   //    true, then throw a TypeError.
   if (opts.allowShared === false && types.isSharedArrayBuffer(V.buffer)) {
-    webidl.errors.exception({
+    throw webidl.errors.exception({
       header: 'ArrayBuffer',
       message: 'SharedArrayBuffer is not allowed.'
     })
@@ -582,7 +556,7 @@ webidl.converters.DataView = function (V, opts = {}) {
   // 1. If Type(V) is not Object, or V does not have a
   //    [[DataView]] internal slot, then throw a TypeError.
   if (webidl.util.Type(V) !== 'Object' || !types.isDataView(V)) {
-    webidl.errors.exception({
+    throw webidl.errors.exception({
       header: 'DataView',
       message: 'Object is not a DataView.'
     })
@@ -593,7 +567,7 @@ webidl.converters.DataView = function (V, opts = {}) {
   //    IsSharedArrayBuffer(V.[[ViewedArrayBuffer]]) is true,
   //    then throw a TypeError.
   if (opts.allowShared === false && types.isSharedArrayBuffer(V.buffer)) {
-    webidl.errors.exception({
+    throw webidl.errors.exception({
       header: 'ArrayBuffer',
       message: 'SharedArrayBuffer is not allowed.'
     })
diff --git a/lib/fileapi/filereader.js b/lib/fileapi/filereader.js
index fa18e8eb593..2bc2c46ac6a 100644
--- a/lib/fileapi/filereader.js
+++ b/lib/fileapi/filereader.js
@@ -37,9 +37,7 @@ class FileReader extends EventTarget {
    * @param {import('buffer').Blob} blob
    */
   readAsArrayBuffer (blob) {
-    if (!(this instanceof FileReader)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, FileReader)
 
     if (arguments.length === 0) {
       throw new TypeError(
@@ -59,9 +57,7 @@ class FileReader extends EventTarget {
    * @param {import('buffer').Blob} blob
    */
   readAsBinaryString (blob) {
-    if (!(this instanceof FileReader)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, FileReader)
 
     if (arguments.length === 0) {
       throw new TypeError(
@@ -82,9 +78,7 @@ class FileReader extends EventTarget {
    * @param {string?} encoding
    */
   readAsText (blob, encoding = undefined) {
-    if (!(this instanceof FileReader)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, FileReader)
 
     if (arguments.length === 0) {
       throw new TypeError(
@@ -108,9 +102,7 @@ class FileReader extends EventTarget {
    * @param {import('buffer').Blob} blob
    */
   readAsDataURL (blob) {
-    if (!(this instanceof FileReader)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, FileReader)
 
     if (arguments.length === 0) {
       throw new TypeError(
@@ -166,9 +158,7 @@ class FileReader extends EventTarget {
    * @see https://w3c.github.io/FileAPI/#dom-filereader-readystate
    */
   get readyState () {
-    if (!(this instanceof FileReader)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, FileReader)
 
     switch (this[kState]) {
       case 'empty': return this.EMPTY
@@ -181,9 +171,7 @@ class FileReader extends EventTarget {
    * @see https://w3c.github.io/FileAPI/#dom-filereader-result
    */
   get result () {
-    if (!(this instanceof FileReader)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, FileReader)
 
     // The result attribute’s getter, when invoked, must return
     // this's result.
@@ -194,9 +182,7 @@ class FileReader extends EventTarget {
    * @see https://w3c.github.io/FileAPI/#dom-filereader-error
    */
   get error () {
-    if (!(this instanceof FileReader)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, FileReader)
 
     // The error attribute’s getter, when invoked, must return
     // this's error.
@@ -204,17 +190,13 @@ class FileReader extends EventTarget {
   }
 
   get onloadend () {
-    if (!(this instanceof FileReader)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, FileReader)
 
     return this[kEvents].loadend
   }
 
   set onloadend (fn) {
-    if (!(this instanceof FileReader)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, FileReader)
 
     if (typeof fn === 'function') {
       this[kEvents].loadend = fn
@@ -224,17 +206,13 @@ class FileReader extends EventTarget {
   }
 
   get onerror () {
-    if (!(this instanceof FileReader)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, FileReader)
 
     return this[kEvents].error
   }
 
   set onerror (fn) {
-    if (!(this instanceof FileReader)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, FileReader)
 
     if (typeof fn === 'function') {
       this[kEvents].error = fn
@@ -244,17 +222,13 @@ class FileReader extends EventTarget {
   }
 
   get onloadstart () {
-    if (!(this instanceof FileReader)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, FileReader)
 
     return this[kEvents].loadstart
   }
 
   set onloadstart (fn) {
-    if (!(this instanceof FileReader)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, FileReader)
 
     if (typeof fn === 'function') {
       this[kEvents].loadstart = fn
@@ -264,17 +238,13 @@ class FileReader extends EventTarget {
   }
 
   get onprogress () {
-    if (!(this instanceof FileReader)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, FileReader)
 
     return this[kEvents].progress
   }
 
   set onprogress (fn) {
-    if (!(this instanceof FileReader)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, FileReader)
 
     if (typeof fn === 'function') {
       this[kEvents].progress = fn
@@ -284,17 +254,13 @@ class FileReader extends EventTarget {
   }
 
   get onload () {
-    if (!(this instanceof FileReader)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, FileReader)
 
     return this[kEvents].load
   }
 
   set onload (fn) {
-    if (!(this instanceof FileReader)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, FileReader)
 
     if (typeof fn === 'function') {
       this[kEvents].load = fn
@@ -304,17 +270,13 @@ class FileReader extends EventTarget {
   }
 
   get onabort () {
-    if (!(this instanceof FileReader)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, FileReader)
 
     return this[kEvents].abort
   }
 
   set onabort (fn) {
-    if (!(this instanceof FileReader)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, FileReader)
 
     if (typeof fn === 'function') {
       this[kEvents].abort = fn
diff --git a/lib/fileapi/progressevent.js b/lib/fileapi/progressevent.js
index ab3c6191e2d..778cf224c6a 100644
--- a/lib/fileapi/progressevent.js
+++ b/lib/fileapi/progressevent.js
@@ -22,25 +22,19 @@ class ProgressEvent extends Event {
   }
 
   get lengthComputable () {
-    if (!(this instanceof ProgressEvent)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, ProgressEvent)
 
     return this[kState].lengthComputable
   }
 
   get loaded () {
-    if (!(this instanceof ProgressEvent)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, ProgressEvent)
 
     return this[kState].loaded
   }
 
   get total () {
-    if (!(this instanceof ProgressEvent)) {
-      throw new TypeError('Illegal invocation')
-    }
+    webidl.brandCheck(this, ProgressEvent)
 
     return this[kState].total
   }
diff --git a/types/webidl.d.ts b/types/webidl.d.ts
new file mode 100644
index 00000000000..c284c44ea3e
--- /dev/null
+++ b/types/webidl.d.ts
@@ -0,0 +1,208 @@
+// These types are not exported, and are only used internally
+
+/**
+ * Take in an unknown value and return one that is of type T
+ */
+type Converter<T> = (object: unknown) => T
+
+type SequenceConverter<T> = (object: unknown) => T[]
+
+type RecordConverter<K extends string, V> = (object: unknown) => Record<K, V>
+
+interface ConvertToIntOpts {
+  clamp?: boolean
+  enforceRange?: boolean
+}
+
+interface WebidlErrors {
+  exception (opts: { header: string, message: string }): TypeError
+  /**
+   * @description Throw an error when conversion from one type to another has failed
+   */
+  conversionFailed (opts: {
+    prefix: string
+    argument: string
+    types: string[]
+  }): TypeError
+  /**
+   * @description Throw an error when an invalid argument is provided
+   */
+  invalidArgument (opts: {
+    prefix: string
+    value: string
+    type: string
+  }): TypeError
+}
+
+interface WebidlUtil {
+  /**
+   * @see https://tc39.es/ecma262/#sec-ecmascript-data-types-and-values
+   */
+  Type (object: unknown):
+    | 'Undefined'
+    | 'Boolean'
+    | 'String'
+    | 'Symbol'
+    | 'Number'
+    | 'BigInt'
+    | 'Null'
+    | 'Object'
+
+  /**
+   * @see https://webidl.spec.whatwg.org/#abstract-opdef-converttoint
+   */
+  ConvertToInt (
+    V: unknown,
+    bitLength: number,
+    signedness: 'signed' | 'unsigned',
+    opts?: ConvertToIntOpts
+  ): number
+
+  /**
+   * @see https://webidl.spec.whatwg.org/#abstract-opdef-converttoint
+   */
+  IntegerPart (N: number): number
+}
+
+interface WebidlConverters {
+  /**
+   * @see https://webidl.spec.whatwg.org/#es-DOMString
+   */
+  DOMString (V: unknown, opts?: {
+    legacyNullToEmptyString: boolean
+  }): string
+
+  /**
+   * @see https://webidl.spec.whatwg.org/#es-ByteString
+   */
+  ByteString (V: unknown): string
+
+  /**
+   * @see https://webidl.spec.whatwg.org/#es-USVString
+   */
+  USVString (V: unknown): string
+
+  /**
+   * @see https://webidl.spec.whatwg.org/#es-boolean
+   */
+  boolean (V: unknown): boolean
+
+  /**
+   * @see https://webidl.spec.whatwg.org/#es-any
+   */
+  any <Value>(V: Value): Value
+
+  /**
+   * @see https://webidl.spec.whatwg.org/#es-long-long
+   */
+  ['long long'] (V: unknown): number
+
+  /**
+   * @see https://webidl.spec.whatwg.org/#es-unsigned-long-long
+   */
+  ['unsigned long long'] (V: unknown): number
+
+  /**
+   * @see https://webidl.spec.whatwg.org/#es-unsigned-short
+   */
+  ['unsigned short'] (V: unknown): number
+
+  /**
+   * @see https://webidl.spec.whatwg.org/#idl-ArrayBuffer
+   */
+  ArrayBuffer (V: unknown): ArrayBufferLike
+  ArrayBuffer (V: unknown, opts: { allowShared: false }): ArrayBuffer
+
+  /**
+   * @see https://webidl.spec.whatwg.org/#es-buffer-source-types
+   */
+  TypedArray (
+    V: unknown,
+    TypedArray: NodeJS.TypedArray | ArrayBufferLike
+  ): NodeJS.TypedArray | ArrayBufferLike
+  TypedArray (
+    V: unknown,
+    TypedArray: NodeJS.TypedArray | ArrayBufferLike,
+    opts?: { allowShared: false }
+  ): NodeJS.TypedArray | ArrayBuffer
+
+  /**
+   * @see https://webidl.spec.whatwg.org/#es-buffer-source-types
+   */
+  DataView (V: unknown, opts?: { allowShared: boolean }): DataView
+
+  /**
+   * @see https://webidl.spec.whatwg.org/#BufferSource
+   */
+  BufferSource (
+    V: unknown,
+    opts?: { allowShared: boolean }
+  ): NodeJS.TypedArray | ArrayBufferLike | DataView
+
+  ['sequence<ByteString>']: SequenceConverter<string>
+  
+  ['sequence<sequence<ByteString>>']: SequenceConverter<string[]>
+
+  ['record<ByteString, ByteString>']: RecordConverter<string, string>
+
+  [Key: string]: (...args: any[]) => unknown
+}
+
+export interface Webidl {
+  errors: WebidlErrors
+  util: WebidlUtil
+  converters: WebidlConverters
+
+  /**
+   * @description Performs a brand-check on {@param V} to ensure it is a
+   * {@param cls} object.
+   */
+  brandCheck <Interface>(V: unknown, cls: Interface): asserts V is Interface
+
+  /**
+   * @see https://webidl.spec.whatwg.org/#es-sequence
+   * @description Convert a value, V, to a WebIDL sequence type.
+   */
+  sequenceConverter <Type>(C: Converter<Type>): SequenceConverter<Type>
+
+  /**
+   * @see https://webidl.spec.whatwg.org/#es-to-record
+   * @description Convert a value, V, to a WebIDL record type.
+   */
+  recordConverter <K extends string, V>(
+    keyConverter: Converter<K>,
+    valueConverter: Converter<V>
+  ): RecordConverter<K, V>
+
+  /**
+   * Similar to {@link Webidl.brandCheck} but allows skipping the check if third party
+   * interfaces are allowed.
+   */
+  interfaceConverter <Interface>(cls: Interface): (
+    V: unknown,
+    opts?: { strict: boolean }
+  ) => asserts V is typeof cls
+
+  // TODO(@KhafraDev): a type could likely be implemented that can infer the return type
+  // from the converters given?
+  /**
+   * Converts a value, V, to a WebIDL dictionary types. Allows limiting which keys are
+   * allowed, values allowed, optional and required keys. Auto converts the value to
+   * a type given a converter.
+   */
+  dictionaryConverter (converters: {
+    key: string,
+    defaultValue?: unknown,
+    required?: boolean,
+    converter: (...args: unknown[]) => unknown,
+    allowedValues?: unknown[]
+  }[]): (V: unknown) => Record<string, unknown>
+
+  /**
+   * @see https://webidl.spec.whatwg.org/#idl-nullable-type
+   * @description allows a type, V, to be null
+   */
+  nullableConverter <T>(
+    converter: Converter<T>
+  ): (V: unknown) => ReturnType<typeof converter> | null
+}