const list = [
      {"className": "花花5555", "gradeName": "畢業班"},
      {"className": "中ei班", "gradeName": "畢業班"},
      {"className": "花花班5", "gradeName": "小班"},
      {"className": "花花", "gradeName": "大班"},
      {"className": "花花班", "gradeName": "中班"},
      {"className": "蘋果班", "gradeName": "大班"},
      {"className": "呃呃呃", "gradeName": "中班"},
      {"className": "中二班", "gradeName": "畢業班"},
      {"className": "大一班", "gradeName": "大班"},
      {"className": "大一班1", "gradeName": "畢業班"},
      {"className": "中一班", "gradeName": "畢業班"}
    ]

for (let i = 0; i < list.length; i++) {
  if (list[i].gradeName === '畢業班') {
    list.splice(i, 1)
  }
}

console.log(JSON.stringify(list))

列印結果：[{"className":"中ei班","gradeName":"畢業班"},

{"className":"花花班5","gradeName":"小班"},

{"className":"花花","gradeName":"大班"},

{"className":"花花班","gradeName":"中班"},

{"className":"蘋果班","gradeName":"大班"},

{"className":"呃呃呃","gradeName":"中班"},

{"className":"大一班","gradeName":"大班"},

{"className":"中一班","gradeName":"畢業班"}

]

發現gradeName為‘畢業班’的元素還有，這是為什麼呢？

通過分析陣列知道了：for迴圈依次進行，每次都在加1，即時陣列改變，也是加1，

當i為0時，發現gradename為‘畢業班’，於是刪除，陣列改變了，

繼續i為1時，實際上，是刪除後新陣列的第二個元素，也就是原陣列的第三個元素，通過這可以發現，跳過了原陣列的第二個元素，導致沒有被迴圈出來，被遺忘了！

解決方案：

for (let i = 0; i < list.length; i++) {
  if (list[i].gradeName === '畢業班') {
    list.splice(i, 1)
    i = i - 1                        //滿足條件時不要跳過下一個元素
  }
}

console.log(JSON.stringify(list))

列印結果：

[{"className":"花花班5","gradeName":"小班"},{"className":"花花","gradeName":"大班"},{"className":"花花班","gradeName":"中班"},{"className":"蘋果班","gradeName":"大班"},{"className":"呃呃呃","gradeName":"中班"},{"className":"大一班","gradeName":"大班"}]

gradeName為‘畢業班’的都被過濾掉了！

讓splice小坑了一下！、、、