This is what worked for me with the latest ibm-watson node-sdk,
Install node-sdk with this command
npm install --save ibm-watson
Then, use this code snippet in your app.js or server.js node file to receive the IAM access token
const watson = require('ibm-watson/sdk');
const { IamAuthenticator } = require('ibm-watson/auth');
// to get an IAM Access Token
const authorization = new watson.AuthorizationV1({
  authenticator: new IamAuthenticator({ apikey: '<apikey>' }),
  url: ''
});
authorization.getToken(function (err, token) {
  if (!token) {
    console.log('error: ', err);
  } else {
    console.log('token: ', token);
  }
});
You can also directly use the IamAuthenticator with Speech to Text 
const fs = require('fs');
const SpeechToTextV1 = require('ibm-watson/speech-to-text/v1');
const { IamAuthenticator } = require('ibm-watson/auth');
const speechToText = new SpeechToTextV1({
  authenticator: new IamAuthenticator({ apikey: '<apikey>' }),
  url: 'https://stream.watsonplatform.net/speech-to-text/api/'
});
const params = {
  // From file
  audio: fs.createReadStream('./resources/speech.wav'),
  contentType: 'audio/l16; rate=44100'
};
speechToText.recognize(params)
  .then(response => {
    console.log(JSON.stringify(response.result, null, 2));
  })
  .catch(err => {
    console.log(err);
  });
// or streaming
fs.createReadStream('./resources/speech.wav')
  .pipe(speechToText.recognizeUsingWebSocket({ contentType: 'audio/l16; rate=44100' }))
  .pipe(fs.createWriteStream('./transcription.txt'));