CODE EXAMPLE FOR JAVASCRIPT

express cors specific origins

let allowedOrigins = ['http://localhost:8080', 'http://testsite.com'];

app.use(cors({
  origin: (origin, callback) => {
    if(!origin) return callback(null, true);
    if(allowedOrigins.indexOf(origin) === -1){ // If a specific origin isn’t found on the list of allowed origins
      let message = 'The CORS policy for this application doesn’t allow access from origin ' + origin;
      return callback(new Error(message ), false);
    }
    return callback(null, true);
  }
}));