Use static factories to create NodeJS buffers

Previously code always used constructor to create NodeJS buffers.
Constructor is overloaded to create buffer from an array,
another buffer, string or with specified size. It is deprecated in
newer NodeJS versions in favor of static factories like `Buffer.alloc()`
and `Buffer.from()`. First allocates a buffer of the specified size.
Second creates buffer based on the given string, array or another buffer.

This commit makes code use static factories instead of the constructor,
when available. This makes construction of buffers work in older NodeJS
environments that only have the constructor and new environments, that
potentially only have static factories.

Author: lutovich

src/v1/internal/buf.js

@@ -511,7 +511,7 @@ class CombinedBuffer extends BaseBuffer {
  */
 class NodeBuffer extends BaseBuffer {
   constructor(arg) {
-    let buffer = arg instanceof _node.Buffer ? arg : new _node.Buffer(arg);
+    const buffer = arg instanceof _node.Buffer ? arg : newNodeJSBuffer(arg);
     super(buffer.length);
     this._buffer = buffer;
   }
@@ -559,6 +559,16 @@ class NodeBuffer extends BaseBuffer {
   }
 }
 
+function newNodeJSBuffer(arg) {
+  if (typeof arg === 'number' && typeof _node.Buffer.alloc === 'function') {
+    // use static factory function present in newer NodeJS versions to allocate new buffer with specified size
+    return _node.Buffer.alloc(arg);
+  } else {
+    // fallback to the old, potentially deprecated constructor
+    return new _node.Buffer(arg);
+  }
+}
+
 // Use HeapBuffer by default, unless Buffer API is available, see below
 let _DefaultBuffer = HeapBuffer;
 try {

src/v1/internal/utf8.js

@@ -20,21 +20,28 @@
 // This module defines a cross-platform UTF-8 encoder and decoder that works
 // with the Buffer API defined in buf.js
 
-import {alloc, NodeBuffer, HeapBuffer, CombinedBuffer} from "./buf";
+import {alloc, CombinedBuffer, HeapBuffer, NodeBuffer} from './buf';
 import {StringDecoder} from 'string_decoder';
 import {newError} from './../error';
+
 let platformObj = {};
 
 
 try {
   // This will throw an exception is 'buffer' is not available
   require.resolve("buffer");
-  let decoder = new StringDecoder('utf8');
-  let node = require("buffer");
+  const decoder = new StringDecoder('utf8');
+  const node = require('buffer');
+
+  // use static factory function present in newer NodeJS versions to create a buffer containing the given string
+  // or fallback to the old, potentially deprecated constructor
+  const newNodeJSBuffer = typeof node.Buffer.from === 'function'
+    ? str => node.Buffer.from(str, 'utf8')
+    : str => new node.Buffer(str, 'utf8');
 
   platformObj = {
     "encode": function (str) {
-      return new NodeBuffer(new node.Buffer(str, "UTF-8"));
+      return new NodeBuffer(newNodeJSBuffer(str));
     },
     "decode": function (buffer, length) {
       if (buffer instanceof NodeBuffer) {