这两个this什么规律

Question

Page({       onLoad(){           console.log(this)//this一           wx.request({               url: 'https://c.y.qq.com/musichall/fcgi-bin/fcg_yqqhomepagerecommend.fcg?g_tk=1844339964&uin=3278805836&format=json&inCharset=utf-8&outCharset=utf-8&notice=0',              success(res) {             console.log(this)//this二                        }           })      } })这是微信小程序的js脚本。为何第一个this指向page对象；而第二个this又是指向success函数本身？