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      • JavaScript教程之ES6入門系列 ----- 對象的遍歷

      • 2019-06-13 08:13 來源:未知

      工作中遍歷對象是家常便飯了,遍歷數組的方法五花八門, 然而很多小伙伴是不是和我之前一樣只會用for ...in....

      來遍歷對象呢, 今天給大家介紹五種遍歷對象屬性的方法:

      • 1, 最常用的for  in   
      1. 它可以便利對象本身及其繼承自原型上的可枚舉屬性,
      2. 過濾掉原型上的屬性可以用hasOwnProperty(屬性名)來判斷是否是本身的屬性,
      3. 對象的每一個屬性都有它的描述,可以用Object.getOwnPropertyDescriptors(對象, 屬性名)來查看對象的某個屬性的描述,可以知道其是否是可枚舉, 可寫,可配置
      • 2, Object.keys(obj)
      1. 是不是有點眼熟,和數組的keys方法很像, 返回一個數組
      2. 這個數組包含自身的所有可枚舉屬性,不包含原型鏈上的屬性以及Symbol屬性
      3. 這個數組是可迭代的,也就是部署了iterator接口,可以用for...of遍歷
      • 3, Object.getOwnPropertyNames(obj)
      1. 返回一個數組
      2. 包含自身的所有屬性,包括不可枚舉的屬性,但不包括Symbol屬性
      • 4  Object.getOwnPropertySymbols(obj)
      1. 返回一個數組
      2. 包含自身的所有Symbol屬性
      • 5  Reflect.ownKeys(obj)
      1. 返回一個數組
      2. 一般不會用, 包含自身的所有屬性, 不管是否為Symbol屬性, 也不管是否可枚舉

      插播 :           Symbol   是 es6  新增的一種基本數據類型,  es5的基本數據有5種, 所以新增后有6種基本數據類型

             在Symbol出現之前,對象的屬性名只能為字符串, 容易造成屬性名沖突, 而Symbol 是獨一無二的,

          所以用Symbol 作為屬性名一定不會沖突。

            格式    const s = Symbol()    , 切記前面不用加new,  因為new 操作符會返回一個對象,而Symbol是

          原始值。Symbol() === Symbol()   // false.

       

      拓展題:        typeof   1234n   =   ?     

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