perf: improve encoding

lib/fetch/body.js

@@ -25,6 +25,8 @@ function extractBody (object, keepalive = false) {
     ReadableStream = require('stream/web').ReadableStream
   }
 
+  const textEncoder = new TextEncoder()
+
   // 1. Let stream be null.
   let stream = null
 
@@ -41,7 +43,7 @@ function extractBody (object, keepalive = false) {
     stream = new ReadableStream({
       async pull (controller) {
         controller.enqueue(
-          typeof source === 'string' ? new TextEncoder().encode(source) : source
+          typeof source === 'string' ? textEncoder.encode(source) : source
         )
         queueMicrotask(() => readableStreamClose(controller))
       },
@@ -108,17 +110,15 @@ function extractBody (object, keepalive = false) {
     // Set action to this step: run the multipart/form-data
     // encoding algorithm, with object’s entry list and UTF-8.
     action = async function * (object) {
-      const enc = new TextEncoder()
-
       for (const [name, value] of object) {
         if (typeof value === 'string') {
-          yield enc.encode(
+          yield textEncoder.encode(
             prefix +
               `; name="${escape(normalizeLinefeeds(name))}"` +
               `\r\n\r\n${normalizeLinefeeds(value)}\r\n`
           )
         } else {
-          yield enc.encode(
+          yield textEncoder.encode(
             prefix +
               `; name="${escape(normalizeLinefeeds(name))}"` +
               (value.name ? `; filename="${escape(value.name)}"` : '') +
@@ -130,11 +130,11 @@ function extractBody (object, keepalive = false) {
 
           yield * value.stream()
 
-          yield enc.encode('\r\n')
+          yield textEncoder.encode('\r\n')
         }
       }
 
-      yield enc.encode(`--${boundary}--`)
+      yield textEncoder.encode(`--${boundary}--`)
     }
 
     // Set source to object.

lib/fetch/headers.js

@@ -47,13 +47,16 @@ function fill (headers, object) {
       // 2. Append (header’s first item, header’s second item) to headers.
       headers.append(header[0], header[1])
     }
-  } else if (typeof object === 'object' && object !== null) {
+  } else if (object !== null && typeof object === 'object') {
     // Note: null should throw
 
     // 2. Otherwise, object is a record, then for each key → value in object,
     //    append (key, value) to headers
-    for (const [key, value] of Object.entries(object)) {
-      headers.append(key, value)
+    const keys = Object.keys(object)
+    const keysLength = keys.length
+
+    for (let i = 0; i < keysLength; i++) {
+      headers.append(keys[i], object[keys[i]])
     }
   } else {
     throw webidl.errors.conversionFailed({