express 跨域访问

//允许跨域访问
app.all('*', function(req, res, next) {
    res.header('Access-Control-Allow-Origin', '*');
    res.header('Access-Control-Allow-Headers', 'Content-Type, Content-Length, Authorization, Accept, X-Requested-With');
    res.header('Access-Control-Allow-Methods', 'PUT, POST, GET, DELETE, OPTIONS');
    res.header('Content-Type', 'application/json; charset=utf-8');
    if (req.method === 'OPTIONS') {
        res.sendStatus(200);
    } else {
        next();
    }
});