node.js express配置允许跨域

app.all(‘*‘, function(req, res, next) { ?????res.header("Access-Control-Allow-Origin", "*"); ?????res.header("Access-Control-Allow-Headers", "X-Requested-With"); ?????res.header("Access-Control-Allow-Methods","PUT,POST,GET,DELETE,OPTIONS"); ?????res.header("X-Powered-By",‘ 3.2.1‘) ?????res.header("Content-Type", "application/json;charset=utf-8"); ?????next(); ?});