JS: Switch from `new Buffer` to `Buffer.from`

Summary:
Constructing `Buffer` using the constructor [[https://nodesource.com/blog/understanding-the-buffer-deprecation-in-node-js-10/ | has been deprecated in Node 10 due to security considerations]].

This is a simple and straightforward conversion.

Reviewed By: mjesun

Differential Revision: D13080655

fbshipit-source-id: 100d8f28c3b255422b26e820aaadcc4f32f41e0d

RNTester/js/websocket_test_server.js

@@ -35,7 +35,7 @@ server.on('connection', ws => {
     console.log('Received message:', message);
     console.log('Cookie:', ws.upgradeReq.headers.cookie);
     if (respondWithBinary) {
-      message = new Buffer(message);
+      message = Buffer.from(message);
     }
     if (message === 'getImage') {
       message = fs.readFileSync(path.resolve(__dirname, 'flux@3x.png'));

local-cli/generator/promptSync.js

@@ -43,7 +43,7 @@ function create() {
       process.stdin.setRawMode(true);
     }
 
-    var buf = new Buffer(3);
+    var buf = Buffer.from(3);
     var str = '',
       character,
       read;
@@ -62,7 +62,7 @@ function create() {
           insert = str.length;
           process.stdout.write('\u001b[2K\u001b[0G' + ask + str);
           process.stdout.write('\u001b[' + (insert + ask.length + 1) + 'G');
-          buf = new Buffer(3);
+          buf = Buffer.from(3);
         }
         continue; // any other 3 character sequence is ignored
       }

local-cli/server/util/copyToClipBoard.js

@@ -23,15 +23,15 @@ function copyToClipBoard(content) {
   switch (process.platform) {
     case 'darwin':
       var child = spawn('pbcopy', []);
-      child.stdin.end(new Buffer(content, 'utf8'));
+      child.stdin.end(Buffer.from(content, 'utf8'));
       return true;
     case 'win32':
       var child = spawn('clip', []);
-      child.stdin.end(new Buffer(content, 'utf8'));
+      child.stdin.end(Buffer.from(content, 'utf8'));
       return true;
     case 'linux':
       var child = spawn(xsel, ['--clipboard', '--input']);
-      child.stdin.end(new Buffer(content, 'utf8'));
+      child.stdin.end(Buffer.from(content, 'utf8'));
       return true;
     default:
       return false;