js对象遍历顺序问题?
用Object.keys遍历对象key,如果对象中不包含key为number类型的话能否保持遍历顺序?现在要改代码话发现要改的地方挺多.
回答
非数组下标型的 key 是按创建时间返回的，所以应该是不能。
ECMA-262的官方描述：
9.1.11 [[OwnPropertyKeys]] ( )When the [[OwnPropertyKeys]] internal method of O is called, the following steps are taken:
1. Return ! OrdinaryOwnPropertyKeys(O).
9.1.11.1 OrdinaryOwnPropertyKeys ( O )When the abstract operation OrdinaryOwnPropertyKeys is called with Object O, the following steps are taken:
1. Let keys be a new empty List.
2. For each own property key P of O such that P is an array index, in ascending numeric index order, do
a. Add P as the last element of keys.
3. For each own property key P of O such that Type(P) is String and P is not an array index, in ascending
chronological order of property creation, do
a. Add P as the last element of keys.
4. For each own property key P of O such that Type(P) is Symbol, in ascending chronological order of property
creation, do
a. Add P as the last element of keys.
5. Return keys.
对象键是没有顺序的，ES6 Map 的 keys 会按插入顺序
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