JavaScript对象的长度 - Length of a JavaScript object

问题：

I have a JavaScript object, is there a built-in or accepted best practice way to get the length of this object? 我有一个JavaScript对象，是否有内置的或公认的最佳实践方法来获取此对象的长度？

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

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解决方案：

参考一： https://stackoom.com/question/1MF/JavaScript对象的长度
参考二： https://oldbug.net/q/1MF/Length-of-a-JavaScript-object