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                合規國際互聯網加速 OSASE為企業客戶提供高速穩定SD-WAN國際加速解決方案。 廣告
                # 對象理解 ## 一、屬性類型 ### 1. 數據屬性 - [[Configurable]] : 默認值為 true - [[Enumerable]] : 默認值為 true - [[Writable]] - [[Value]] ### 2. 訪問器屬性 - [[Configurable]] : 默認值為 true - [[Enumerable]] : 默認值為 true - [[Get]] - [[Set]] > Configurable 能否通過 delete 刪除屬性從而重新定義屬性 能否通過 for-in 循環返回屬性 ## 對象的遍歷 [參考](https://juejin.im/post/5d48c275f265da03b12032a1?utm_source=gold_browser_extension) ## 二、屬性的CRUD #### 遍歷自身可枚舉屬性 返回數組 Object.keys() // 屬性鍵 數組 Object.values() // 屬性值 數組 Object.entries() // 鍵值對 數組 #### 遍歷自身可枚舉屬性 和 原型鏈中的屬性 for..in ``` let simpleColors = { colorA: 'white', colorB: 'black' }; let natureColors = { colorC: 'green', colorD: 'yellow' }; Object.setPrototypeOf(natureColors, simpleColors); Object.keys(natureColors); // => ['colorC', 'colorD'] Object.values(natureColors) Object.entries(natureColors); // [["colorC", "green"], ["colorD", "yellow"]] for (let key in natureColors) { console.log(key) } // => ['colorC', 'colorD', 'colorA', 'colorB'] ``` > Object.setPrototypeOf() 方法設置一個指定的對象的原型 ( 即, 內部[[Prototype]]屬性)到另一個對象或 null。 ### Object.entries() 轉 Map > Object.entries() 返回的格式與Map構造函數接受的格式完全相同:(key,value) ``` let greetings = { morning: 'Good morning', midday: 'Good day', evening: 'Good evening' }; let greetingsMap = new Map(Object.entries(greetings)); greetingsMap.get('morning'); // => 'Good morning' greetingsMap.get('midday'); // => 'Good day' greetingsMap.get('evening'); // => 'Good evening' ``` 普通對象 不是Iterators 不能使用for...of,通常 ``` for (let item of Object.entries(greetings)) { console.log(key) } ``` Map提供了與Object.values()和Object.entries() 等效的方法(只是它們返回Iterators),以便為Map實例提取屬性值或鍵值對: 1. Map.prototype.values() 等價于Object.values() 2. Map.prototype.entries() 等價于Object.entries() ``` // ... [...greetingsMap.values()]; // => ['Good morning', 'Good day', 'Good evening'] [...greetingsMap.entries()]; // => [ ['morning', 'Good morning'], ['midday', 'Good day'], // ['evening', 'Good evening'] ] ``` > greetingsMap.values()和greetingsMap.entries()返回迭代器對象。若要將結果放入數組,擴展運算符…是必要的 ## 創建對象的七種方法 ## 參考文檔 【1】[標準庫—Object 對象-阮一峰](https://mp.weixin.qq.com/s/wuuhbr1OByq85OTgP2XbtA)
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