Express allow CORS

cors.js

module.exports.allowCORS = function(app) {
    var allowCrossDomain = function(req, res, next) {
        res.header('Access-Control-Allow-Origin', '*');
        res.header('Access-Control-Allow-Methods', 'GET,PUT,POST,DELETE');
        res.header('Access-Control-Allow-Headers', 'Content-Type, Authorization');
          
        if ('OPTIONS' == req.method) {
          res.send(200);
        } else {
          next();
        }
    };
    app.use(allowCrossDomain);
};