diff --git a/lib/_http_outgoing.js b/lib/_http_outgoing.js
index f40cf923f9b377..066edc58626eec 100644
--- a/lib/_http_outgoing.js
+++ b/lib/_http_outgoing.js
@@ -165,9 +165,7 @@ ObjectDefineProperty(OutgoingMessage.prototype, '_headers', {
       this[kOutHeaders] = null;
     } else if (typeof val === 'object') {
       const headers = this[kOutHeaders] = ObjectCreate(null);
-      const keys = ObjectKeys(val);
-      for (var i = 0; i < keys.length; ++i) {
-        const name = keys[i];
+      for (name of ObjectKeys(val)) {
         headers[name.toLowerCase()] = [name, val[name]];
       }
     }
@@ -188,9 +186,7 @@ ObjectDefineProperty(OutgoingMessage.prototype, '_headerNames', {
     const headers = this[kOutHeaders];
     if (headers !== null) {
       const out = ObjectCreate(null);
-      const keys = ObjectKeys(headers);
-      for (var i = 0; i < keys.length; ++i) {
-        const key = keys[i];
+      for (key of ObjectKeys(headers)) {
         const val = headers[key][0];
         out[key] = val;
       }
@@ -203,11 +199,10 @@ ObjectDefineProperty(OutgoingMessage.prototype, '_headerNames', {
       const headers = this[kOutHeaders];
       if (!headers)
         return;
-      const keys = ObjectKeys(val);
-      for (var i = 0; i < keys.length; ++i) {
-        const header = headers[keys[i]];
+      for (key of ObjectKeys(val)) {
+        const header = headers[key];
         if (header)
-          header[0] = val[keys[i]];
+          header[0] = val[key];
       }
     }
   }, 'OutgoingMessage.prototype._headerNames is deprecated', 'DEP0066')
@@ -223,9 +218,7 @@ OutgoingMessage.prototype._renderHeaders = function _renderHeaders() {
   const headers = {};
 
   if (headersMap !== null) {
-    const keys = ObjectKeys(headersMap);
-    for (var i = 0, l = keys.length; i < l; i++) {
-      const key = keys[i];
+    for (key of ObjectKeys(headersMap)) {
       headers[headersMap[key][0]] = headersMap[key][1];
     }
   }
@@ -458,8 +451,8 @@ function processHeader(self, state, key, value, validate) {
     validateHeaderName(key);
   if (ArrayIsArray(value)) {
     if (value.length < 2 || !isCookieField(key)) {
-      for (var i = 0; i < value.length; i++)
-        storeHeader(self, state, key, value[i], validate);
+      for (keyValue of value)
+        storeHeader(self, state, key, keyValue, validate);
       return;
     }
     value = value.join('; ');
@@ -558,9 +551,7 @@ OutgoingMessage.prototype.getHeaders = function getHeaders() {
   const headers = this[kOutHeaders];
   const ret = ObjectCreate(null);
   if (headers) {
-    const keys = ObjectKeys(headers);
-    for (var i = 0; i < keys.length; ++i) {
-      const key = keys[i];
+    for (key of ObjectKeys(headers)) {
       const val = headers[key][1];
       ret[key] = val;
     }
@@ -697,11 +688,9 @@ function connectionCorkNT(conn) {
 
 OutgoingMessage.prototype.addTrailers = function addTrailers(headers) {
   this._trailer = '';
-  const keys = ObjectKeys(headers);
   const isArray = ArrayIsArray(headers);
   var field, value;
-  for (var i = 0, l = keys.length; i < l; i++) {
-    var key = keys[i];
+  for (key of ObjectKeys(headers)) {
     if (isArray) {
       field = headers[key][0];
       value = headers[key][1];
@@ -847,15 +836,13 @@ OutgoingMessage.prototype._flushOutput = function _flushOutput(socket) {
     socket.cork();
   }
 
-  const outputLength = this.outputData.length;
-  if (outputLength <= 0)
+  if (this.outputData.length <= 0)
     return undefined;
 
-  const outputData = this.outputData;
   socket.cork();
   let ret;
-  for (var i = 0; i < outputLength; i++) {
-    const { data, encoding, callback } = outputData[i];
+  for (outputDataItem of this.outputData) {
+    const { data, encoding, callback } = outputDataItem;
     ret = socket.write(data, encoding, callback);
   }
   socket.uncork();