perf: always use the same prototype Iterator

lib/fetch/formdata.js

@@ -1,6 +1,6 @@
 'use strict'
 
-const { isBlobLike, makeIterator } = require('./util')
+const { isBlobLike, createIterator } = require('./util')
 const { kState } = require('./symbols')
 const { kEnumerableProperty } = require('../core/util')
 const { File: UndiciFile, FileLike, isFileLike } = require('./file')
@@ -10,6 +10,8 @@ const { File: NativeFile } = require('node:buffer')
 /** @type {globalThis['File']} */
 const File = NativeFile ?? UndiciFile
 
+const makeIterator = createIterator('FormData', kState, 'name', 'value')
+
 // https://xhr.spec.whatwg.org/#formdata
 class FormData {
   constructor (form) {
@@ -158,34 +160,19 @@ class FormData {
   entries () {
     webidl.brandCheck(this, FormData)
 
-    return makeIterator(
-      () => this[kState],
-      'FormData',
-      'key+value',
-      'name', 'value'
-    )
+    return makeIterator(this, 'key+value')
   }
 
   keys () {
     webidl.brandCheck(this, FormData)
 
-    return makeIterator(
-      () => this[kState],
-      'FormData',
-      'key',
-      'name', 'value'
-    )
+    return makeIterator(this, 'key')
   }
 
   values () {
     webidl.brandCheck(this, FormData)
 
-    return makeIterator(
-      () => this[kState],
-      'FormData',
-      'value',
-      'name', 'value'
-    )
+    return makeIterator(this, 'value')
   }
 
   /**
@@ -203,7 +190,7 @@ class FormData {
       )
     }
 
-    for (const [key, value] of this) {
+    for (const [key, value] of makeIterator(this, 'key+value')) {
       callbackFn.call(thisArg, value, key, this)
     }
   }

lib/fetch/headers.js

@@ -1,12 +1,13 @@
 // https://github.com/Ethan-Arrowood/undici-fetch
+// https://github.com/Ethan-Arrowood/undici-fetch
 
 'use strict'
 
 const { kHeadersList, kConstruct } = require('../core/symbols')
 const { kGuard } = require('./symbols')
 const { kEnumerableProperty } = require('../core/util')
 const {
-  makeIterator,
+  createIterator,
   isValidHeaderName,
   isValidHeaderValue
 } = require('./util')
@@ -16,6 +17,8 @@ const assert = require('node:assert')
 const kHeadersMap = Symbol('headers map')
 const kHeadersSortedMap = Symbol('headers map sorted')
 
+const makeIterator = createIterator('Headers', kHeadersSortedMap, 0, 1)
+
 /**
  * @param {number} code
  */
@@ -507,34 +510,19 @@ class Headers {
   keys () {
     webidl.brandCheck(this, Headers)
 
-    return makeIterator(
-      () => this[kHeadersSortedMap],
-      'Headers',
-      'key',
-      0, 1
-    )
+    return makeIterator(this, 'key')
   }
 
   values () {
     webidl.brandCheck(this, Headers)
 
-    return makeIterator(
-      () => this[kHeadersSortedMap],
-      'Headers',
-      'value',
-      0, 1
-    )
+    return makeIterator(this, 'value')
   }
 
   entries () {
     webidl.brandCheck(this, Headers)
 
-    return makeIterator(
-      () => this[kHeadersSortedMap],
-      'Headers',
-      'key+value',
-      0, 1
-    )
+    return makeIterator(this, 'key+value')
   }
 
   /**
@@ -552,7 +540,7 @@ class Headers {
       )
     }
 
-    for (const [key, value] of this) {
+    for (const [key, value] of makeIterator(this, 'key+value')) {
       callbackFn.call(thisArg, value, key, this)
     }
   }

lib/fetch/util.js

@@ -739,18 +739,14 @@ const esIteratorPrototype = Object.getPrototypeOf(Object.getPrototypeOf([][Symbo
 
 /**
  * @see https://webidl.spec.whatwg.org/#dfn-iterator-prototype-object
- * @param {() => unknown} iterator
  * @param {string} name name of the instance
- * @param {'key'|'value'|'key+value'} kind
+ * @param {symbol} kInternalIterator
  * @param {string | number} [keyIndex]
  * @param {string | number} [valueIndex]
  */
-function makeIterator (iterator, name, kind, keyIndex = 0, valueIndex = 1) {
-  const object = {
-    index: 0,
-    kind,
-    target: iterator
-  }
+function createIterator (name, kInternalIterator, keyIndex = 0, valueIndex = 1) {
+  const kInternalObject = Symbol('internal Object')
+
   // The [[Prototype]] internal slot of an iterator prototype object must be %IteratorPrototype%.
   const iteratorObject = Object.create(esIteratorPrototype)
 
@@ -767,17 +763,18 @@ function makeIterator (iterator, name, kind, keyIndex = 0, valueIndex = 1) {
 
       // 5. If object is not a default iterator object for interface,
       //    then throw a TypeError.
-      if (Object.getPrototypeOf(this) !== iteratorObject) {
+      if (typeof this !== 'object' || this === null || !(kInternalObject in this)) {
         throw new TypeError(
           `'next' called on an object that does not implement interface ${name} Iterator.`
         )
       }
+      const state = this[kInternalObject]
 
       // 6. Let index be object’s index.
       // 7. Let kind be object’s kind.
       // 8. Let values be object’s target's value pairs to iterate over.
-      const { index, kind, target } = object
-      const values = target()
+      const { index, kind, target } = state
+      const values = target[kInternalIterator]
 
       // 9. Let len be the length of values.
       const len = values.length
@@ -790,7 +787,7 @@ function makeIterator (iterator, name, kind, keyIndex = 0, valueIndex = 1) {
       // 11. Let pair be the entry in values at index index.
       const { [keyIndex]: key, [valueIndex]: value } = values[index]
       // 12. Set object’s index to index + 1.
-      object.index = index + 1
+      state.index = index + 1
       // 13. Return the iterator result for pair and kind.
       // https://webidl.spec.whatwg.org/#iterator-result
       // 1. Let result be a value determined by the value of kind:
@@ -844,9 +841,26 @@ function makeIterator (iterator, name, kind, keyIndex = 0, valueIndex = 1) {
     configurable: true
   })
 
-  // esIteratorPrototype needs to be the prototype of iteratorObject
-  // which is the prototype of an empty object. Yes, it's confusing.
-  return Object.create(iteratorObject)
+  /**
+   * @param {unknown} target
+   * @param {'key'|'value'|'key+value'} kind
+   */
+  return function (target, kind) {
+    // esIteratorPrototype needs to be the prototype of iteratorObject
+    // which is the prototype of an empty object. Yes, it's confusing.
+    const iterator = Object.create(iteratorObject)
+    Object.defineProperty(iterator, kInternalObject, {
+      value: {
+        target,
+        kind,
+        index: 0
+      },
+      writable: false,
+      enumerable: false,
+      configurable: true
+    })
+    return iterator
+  }
 }
 
 /**
@@ -1365,7 +1379,7 @@ module.exports = {
   sameOrigin,
   normalizeMethod,
   serializeJavascriptValueToJSONString,
-  makeIterator,
+  createIterator,
   isValidHeaderName,
   isValidHeaderValue,
   isErrorLike,