调用前使用npm添加express模块 
var express = require('express');
var app = express();

var urlencodedParser = bodyParser.urlencoded({
 extended: false
})

app.use(express.static('public'));
//allow custom header and CORS
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 , yourHeaderFeild');
 res.header('Access-Control-Allow-Methods', 'PUT, POST, GET, DELETE, OPTIONS');

if(req.method == 'OPTIONS') {
 res.send(200);
 /让options请求快速返回/
 } else {
 next();
 }
});