express.js middleware to support CORS pre-flight requests

node-express-cors-middleware.js

app.use(express.methodOverride());

// ## CORS middleware
// 
// see: http://stackoverflow.com/questions/7067966/how-to-allow-cors-in-express-nodejs
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');
      
    // intercept OPTIONS method
    if ('OPTIONS' == req.method) {
      res.send(200);
    }
    else {
      next();
    }
};
app.use(allowCrossDomain);

Cool stuff with the 'OPTIONS' hack

You might want to look at https://github.com/agrueneberg/Corser

A small note here: a select few versions of Android's native browser, including Gingerbread, will prepend the response body of the OPTIONS call to the response body of the actual call. By default, res.send will include the body 'OK', which causes problems when attempting to parse the body as JSON. To mitigate this issue, use res.send(200, ''), otherwise you'll end up trying to parse 'OK{}'.

You should probably be using res.send(204). The 204 HTTP status indicates "No Content".

I would like to re-iterate what @mwawrusch says: please look at a module like corser and do not use this; this does not fully comply with the CORS specification, where-as a module like corser does (and less LoC for you to maintain in your app, at that).

Don't forget about Access-Control-Allow-Credentials

Thank you !

FYI for newer versions of Express, you will get a warning saying res.send is deprecated. Use res.sendStatus instead

Thanks again ))

WARNING: be aware that for authenticated cors requests, Access-Control-Allow-Origin can't be a wildcard '*'
https://developer.mozilla.org/en-US/docs/Web/HTTP/Access_control_CORS#Credentialed_requests_and_wildcards

Works!

@Lonniebiz please share a snippet of how you solved it.

Thank you so much!!!

Thank you!!

Great, it is helpful.

Very good!

This is Great stuff. it worked for me

Great, it works! Thank you.