im正在学习JSON，并在循环JSON时遇到问题。 这是我的JSON响应

{
"success": 1,"category": [{
    "id": "1","category": "Editorial","created_at": "2019-11-05 18:10:31","firstname": "abc","lastname": "xyz"
},{
    "id": "2","category": "Sports","created_at": "2019-11-05 19:25:50",{
    "id": "3","category": "Health","created_at": "2019-11-05 19:27:23",{
    "id": "4","category": "Food","created_at": "2019-11-05 19:39:17","lastname": "xyz"
}]}

这是我的循环

for(var i = 0; i <= jsonData.category.length; i++){
      console.log(jsonData.category[i]['firstname']);}

它确实在控制台中打印，但它给了我这个错误

  

无法读取未定义的属性“名字”       在Object.success