JavaScript對象的長度 - Length of a JavaScript object

問題：

I have a JavaScript object, is there a built-in or accepted best practice way to get the length of this object? 我有一個JavaScript對象，是否有內置的或公認的最佳實踐方法來獲取此對象的長度？

const myObject = new Object();
myObject["firstname"] = "Gareth";
myObject["lastname"] = "Simpson";
myObject["age"] = 21;

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解決方案：

參考一： https://stackoom.com/question/1MF/JavaScript對象的長度
參考二： https://oldbug.net/q/1MF/Length-of-a-JavaScript-object