如何有效地計算JavaScript中對象的鍵/屬性數量？

問題：

What's the fastest way to count the number of keys/properties of an object? 計算對象的鍵/屬性數的最快方法是什麼？ It it possible to do this without iterating over the object? 是否能夠在不迭代對象的狀況下執行此操做？ ie without doing 即不作

var count = 0;
for (k in myobj) if (myobj.hasOwnProperty(k)) count++;

(Firefox did provide a magic __count__ property, but this was removed somewhere around version 4.) （Firefox確實提供了一個神奇的__count__屬性，但此屬性已在版本4的某個位置刪除。）

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解決方案：

參考一： https://stackoom.com/question/Wns/如何有效地計算JavaScript中對象的鍵-屬性數量
參考二： https://oldbug.net/q/Wns/How-to-efficiently-count-the-number-of-keys-properties-of-an-object-in-JavaScript