遍歷數組的問題---已解決

解決：第一種方式會輸出數組原型中的屬性

HTMLCollection(3) [li, li, li]
0: li
1: li
2: li
length: 3
__proto__: HTMLCollection
item: ƒ item()
length: (...)
namedItem: ƒ namedItem()
constructor: ƒ HTMLCollection()
Symbol(Symbol.iterator): ƒ values()
Symbol(Symbol.toStringTag): "HTMLCollection"
get length: ƒ length()
__proto__: Object

原問題 

    for (let i in bannerLi) {
        bannerLi[i].style.opacity = 0;
    }

用 for in 遍歷數組的時候，會報錯

用循環遍歷顯示正常

    for (let i = 0; i < bannerLi.length; i++) {
        bannerLi[i].style.opacity = 0;
    }

請問大佬們是什麼原因