perf: use class make faster

lib/fetch/util.js

@@ -745,55 +745,72 @@ const esIteratorPrototype = Object.getPrototypeOf(Object.getPrototypeOf([][Symbo
  * @param {string | number} [keyIndex]
  * @param {string | number} [valueIndex]
  */
-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)
+function createFastIterator (name, kInternalIterator, keyIndex = 0, valueIndex = 1) {
+  class FastIterableIterator {
+    /** @type {any} */
+    #target
+    /** @type {'key' | 'value' | 'key+value'} */
+    #kind
+    /** @type {number} */
+    #index
+
+    /**
+     * @see https://webidl.spec.whatwg.org/#dfn-default-iterator-object
+     * @param {unknown} target
+     * @param {'key' | 'value' | 'key+value'} kind
+     */
+    constructor (target, kind) {
+      this.#target = target
+      this.#kind = kind
+      this.#index = 0
+    }
 
-  Object.defineProperty(iteratorObject, 'next', {
-    value: function next () {
+    next () {
       // 1. Let interface be the interface for which the iterator prototype object exists.
-
       // 2. Let thisValue be the this value.
-
       // 3. Let object be ? ToObject(thisValue).
-
       // 4. If object is a platform object, then perform a security
       //    check, passing:
-
       // 5. If object is not a default iterator object for interface,
       //    then throw a TypeError.
-      if (typeof this !== 'object' || this === null || !(kInternalObject in this)) {
+      // Object.getPrototypeOf(this) !== FastIterator.prototype
+      if (typeof this !== 'object' || this === null || !(#target in this)) {
         throw new TypeError(
           `'next' called on an object that does not implement interface ${name} Iterator.`
         )
       }
-      const object = 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[kInternalIterator]
+      const index = this.#index
+      const values = this.#target[kInternalIterator]
 
       // 9. Let len be the length of values.
       const len = values.length
 
       // 10. If index is greater than or equal to len, then return
       //     CreateIterResultObject(undefined, true).
       if (index >= len) {
-        return { value: undefined, done: true }
+        return {
+          value: undefined,
+          done: true
+        }
       }
+
       // 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
+      this.#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:
       let result
-      switch (kind) {
+      switch (this.#kind) {
         case 'key':
           // 1. Let idlKey be pair’s key.
           // 2. Let key be the result of converting idlKey to an
@@ -822,45 +839,37 @@ function createIterator (name, kInternalIterator, keyIndex = 0, valueIndex = 1)
           result = [key, value]
           break
       }
+
       // 2. Return CreateIterResultObject(result, false).
       return {
         value: result,
         done: false
       }
-    },
-    writable: true,
-    enumerable: true,
-    configurable: true
-  })
+    }
+  }
+
+  // https://webidl.spec.whatwg.org/#dfn-iterator-prototype-object
+  // @ts-ignore
+  delete FastIterableIterator.prototype.constructor
+
+  Object.setPrototypeOf(FastIterableIterator.prototype, esIteratorPrototype)
 
-  // The class string of an iterator prototype object for a given interface is the
-  // result of concatenating the identifier of the interface and the string " Iterator".
-  Object.defineProperty(iteratorObject, Symbol.toStringTag, {
-    value: `${name} Iterator`,
-    writable: false,
-    enumerable: false,
-    configurable: true
+  Object.defineProperties(FastIterableIterator.prototype, {
+    [Symbol.toStringTag]: {
+      writable: false,
+      enumerable: false,
+      configurable: true,
+      value: `${name} Iterator`
+    },
+    next: { writable: true, enumerable: true, configurable: true }
   })
 
   /**
    * @param {unknown} target
-   * @param {'key'|'value'|'key+value'} kind
+   * @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
+    return new FastIterableIterator(target, kind)
   }
 }
 
@@ -873,7 +882,7 @@ function createIterator (name, kInternalIterator, keyIndex = 0, valueIndex = 1)
  * @param {string | number} [valueIndex]
  */
 function iteratorMixin (name, object, kInternalIterator, keyIndex = 0, valueIndex = 1) {
-  const makeIterator = createIterator(name, kInternalIterator, keyIndex, valueIndex)
+  const createIterator = createFastIterator(name, kInternalIterator, keyIndex, valueIndex)
 
   const properties = {
     keys: {
@@ -882,7 +891,7 @@ function iteratorMixin (name, object, kInternalIterator, keyIndex = 0, valueInde
       configurable: true,
       value: function keys () {
         webidl.brandCheck(this, object)
-        return makeIterator(this, 'key')
+        return createIterator(this, 'key')
       }
     },
     values: {
@@ -891,7 +900,7 @@ function iteratorMixin (name, object, kInternalIterator, keyIndex = 0, valueInde
       configurable: true,
       value: function values () {
         webidl.brandCheck(this, object)
-        return makeIterator(this, 'value')
+        return createIterator(this, 'value')
       }
     },
     entries: {
@@ -900,7 +909,7 @@ function iteratorMixin (name, object, kInternalIterator, keyIndex = 0, valueInde
       configurable: true,
       value: function entries () {
         webidl.brandCheck(this, object)
-        return makeIterator(this, 'key+value')
+        return createIterator(this, 'key+value')
       }
     },
     forEach: {
@@ -915,7 +924,7 @@ function iteratorMixin (name, object, kInternalIterator, keyIndex = 0, valueInde
             `Failed to execute 'forEach' on '${name}': parameter 1 is not of type 'Function'.`
           )
         }
-        for (const { 0: key, 1: value } of makeIterator(this, 'key+value')) {
+        for (const { 0: key, 1: value } of createIterator(this, 'key+value')) {
           callbackfn.call(thisArg, value, key, this)
         }
       }
@@ -1448,7 +1457,6 @@ module.exports = {
   sameOrigin,
   normalizeMethod,
   serializeJavascriptValueToJSONString,
-  createIterator,
   iteratorMixin,
   isValidHeaderName,
   isValidHeaderValue,