引入express，並設定header頭部資訊

提醒：一定要先加程式碼，然後再引用api

var app = express();
//先加頭部資訊
app.all('*', function(req, res, next) {
    res.header("Access-Control-Allow-Origin", "*");//允許所有來源訪問 
    res.header("Access-Control-Allow-Headers", "X-Requested-With");
    res.header("Access-Control-Allow-Methods","PUT,POST,GET,DELETE,OPTIONS");//允許訪問的方式 
    res.header("X-Powered-By",' 3.2.1')
    res.header("Content-Type", "application/json;charset=utf-8");
    next();
});
//後使用api
app.use(api);