将wx.request包装成云函数格式：

云函数的调用格式是：wx.cloud.callFunction({name:'login',data:{x:1,y:2}}).then()

仿云函数的调用格式是：app.callFunction({name:'login',data:{x:1,y:2}}).then()

两者一模一样。

在app.js里：

url: 'https://xxx.com/applet/',
callFunction: function(args) {
    return new Promise((resolve, reject) => {
      wx.request({
        url: this.url + args.name,
        method: 'POST',
        data: {
          sessionid: this.getSessionid(),//换取openid
          ...args.data
        },
        success: resolve,
        fail: reject
      })
    })
  },

page里index.js

app.callFunction({name:'login',data:{x:1,y:2}}).then(res=>{console.log(res)})

传统后台：nginx+nodejs+koa2+mongo

nginx定义一条路由：'https://xxx.com/applet/'

koa定义一条路由：'login'