Add CORS option

When using the proxy option and loading browser-sync manually via inline script tag it would be nice to have the possibility to check if the server on port 3000 is running, like this:

var url = '//' + location.hostname + ':3000/browser-sync-client.js',
    xhr = new XMLHttpRequest();

xhr.onreadystatechange = function() {
    if(xhr.readyState == 4 && xhr.status == 200) {
        document.write(('<script async="async" src="' + url + '"><\/script>'));
    }
};

xhr.open('HEAD', url, true);
xhr.send();

The problem is that sending the head request is not allowed, because the browser treats the request to the server on port 3000 as a cross-domain request. It would be nice to have an option to configure CORS headers for the browser-sync server.

[shakyShane]

@bclinkinbeard @TeodorKolev also, since 2.16.0 this is supported via the cors option.

const bs = require('browser-sync').create();

bs.init({
    server: './app',
    cors: true
});

[bclinkinbeard]

@TeodorKolev you need to add this to your BS config:

middleware: function (req, res, next) {
  res.setHeader('Access-Control-Allow-Origin', '*');
  next();
}