ERROR TypeError: this.X is not a function when trying to call it with Ajax

I’m trying to call successLogin() function as below from an Ajax code segment using Typescript in an Ionic v3 project. But it gives this.successLogin() is not a function error. Can anyone suggest a workaround?

signin() 
  {
    var ajaxResp = $.ajax({
      type: "POST",
      url: "XXX",
      data: { 
        'uid': "50", 
        'pass': "100" 
    }
      })
    .done(function(response){
      let js = JSON.parse(response).data;      
      console.log(js);
      this.successLogin(js);
    });
  }

successLogin(msg){
  console.log(msg);
}

I attached an image of the error as well.

error

Source: AngularJS