lib: refactor internal/freelist

PR-URL: https://github.com/nodejs/node/pull/11406
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Michaël Zasso <targos@protonmail.com>

lib/internal/freelist.js

@@ -1,24 +1,25 @@
 'use strict';
 
-// This is a free list to avoid creating so many of the same object.
-exports.FreeList = function(name, max, constructor) {
-  this.name = name;
-  this.constructor = constructor;
-  this.max = max;
-  this.list = [];
-};
-
-
-exports.FreeList.prototype.alloc = function() {
-  return this.list.length ? this.list.pop() :
-                            this.constructor.apply(this, arguments);
-};
-
-
-exports.FreeList.prototype.free = function(obj) {
-  if (this.list.length < this.max) {
-    this.list.push(obj);
-    return true;
+class FreeList {
+  constructor(name, max, ctor) {
+    this.name = name;
+    this.ctor = ctor;
+    this.max = max;
+    this.list = [];
   }
-  return false;
-};
+
+  alloc() {
+    return this.list.length ? this.list.pop() :
+                              this.ctor.apply(this, arguments);
+  }
+
+  free(obj) {
+    if (this.list.length < this.max) {
+      this.list.push(obj);
+      return true;
+    }
+    return false;
+  }
+}
+
+module.exports = {FreeList};