在app.js的最开始加上

app.all('*', (req, res, next) => {    res.header("Access-Control-Allow-Origin", req.headers.origin || '*');    res.header("Access-Control-Allow-Headers", "Content-Type, Authorization, X-Requested-With");    res.header("Access-Control-Allow-Methods", "PUT,POST,GET,DELETE,OPTIONS");    res.header("Access-Control-Allow-Credentials", true); // 可以带cookies    if(req.method == 'OPTIONS') {        res.sendStatus(200);    } else {        next();    }});