微信小程序错误this.setData报错及解决过程

thirdScriptError
this.setData is not a function;at pages/index/index onLoad function;at api getSystemInfo suess callback function
TypeError: this.setData is not a function

onLoad: function () {
  wx.getSystemInfo({
   suess: function (res) {
    this.setData({
     lang: res.language
    })
    console.log(res.language)
   }
  })

onLoad: function() {
  wx.getSystemInfo({
    suess: (res) = >{
      this.setData({箭头函数的this始终指向函数定义时的this lang: res.language
      }) console.log(res.language)
    }
  })

onLoad: function () {
  var that=this;
  wx.getSystemInfo({
   suess: function (res) {
    that.setData({
     lang: res.language
    })
    console.log(res.language)
   }
  })

'use strict';
var obj = {
 i: 10,
 b: () => console.log(this.i, this),
 c: function() {
  console.log(this.i, this);
 }
}
obj.b(); // prints undefined, Window {...} (or the global object)
obj.c(); // prints 10, Object {...}