Calling Microsoft Graph API from an Azure Function using JavaScript - getToken Function

getToken.js

var adal = require('adal-node');

const TENANT = "{tenant-name-here}.onmicrosoft.com";
const CLIENT_ID = "{Application-id-here}";
const CLIENT_SECRET = "{Application-key-here}";

function getToken() {
  return new Promise((resolve, reject) => {
    const authContext = new adal.AuthenticationContext(`https://login.microsoftonline.com/${TENANT}`);
    authContext.acquireTokenWithClientCredentials(GRAPH_URL, CLIENT_ID, CLIENT_SECRET, (err, tokenRes) => {
      if (err) { reject(err); }
      resolve(tokenRes.accessToken);
    });
  });
}

var adal = require('adal-node'); => const adal = require('adal-node');

Seems like you are mixing ECMAScript's together.