streams: refactor BufferList into ES6 class

PR-URL: https://github.com/nodejs/node/pull/12644
Reviewed-By: Brian White <mscdex@mscdex.net>

lib/internal/streams/BufferList.js

@@ -2,15 +2,14 @@
 
 const Buffer = require('buffer').Buffer;
 
-module.exports = BufferList;
-
-function BufferList() {
+module.exports = class BufferList {
+  constructor() {
     this.head = null;
     this.tail = null;
     this.length = 0;
   }
 
-BufferList.prototype.push = function(v) {
+  push(v) {
     const entry = { data: v, next: null };
     if (this.length > 0)
       this.tail.next = entry;
@@ -18,17 +17,17 @@ BufferList.prototype.push = function(v) {
       this.head = entry;
     this.tail = entry;
     ++this.length;
-};
+  }
 
-BufferList.prototype.unshift = function(v) {
+  unshift(v) {
     const entry = { data: v, next: this.head };
     if (this.length === 0)
       this.tail = entry;
     this.head = entry;
     ++this.length;
-};
+  }
 
-BufferList.prototype.shift = function() {
+  shift() {
     if (this.length === 0)
       return;
     const ret = this.head.data;
@@ -38,14 +37,14 @@ BufferList.prototype.shift = function() {
       this.head = this.head.next;
     --this.length;
     return ret;
-};
+  }
 
-BufferList.prototype.clear = function() {
+  clear() {
     this.head = this.tail = null;
     this.length = 0;
-};
+  }
 
-BufferList.prototype.join = function(s) {
+  join(s) {
     if (this.length === 0)
       return '';
     var p = this.head;
@@ -53,9 +52,9 @@ BufferList.prototype.join = function(s) {
     while (p = p.next)
       ret += s + p.data;
     return ret;
-};
+  }
 
-BufferList.prototype.concat = function(n) {
+  concat(n) {
     if (this.length === 0)
       return Buffer.alloc(0);
     if (this.length === 1)
@@ -69,4 +68,5 @@ BufferList.prototype.concat = function(n) {
       p = p.next;
     }
     return ret;
+  }
 };