使用带有括号符号的hasOwnProperty的Mdn参考

问题描述

我在javascript中使用了以下代码:

I am using the following code in javascript:

let group = false;
let internalId = "someString";
let appliedTo = "someOtherString";
let keyToGroupBy = true === group ? internalId : appliedTo;

if(grouped.hasOwnProperty([keyToGroupBy])) {
   ...
}

有人可以提供参考，说明为什么在keyToGroupBy中使用方括号可以在mdn中更好地工作吗?这是被认为是hack(偶然)还是它是常用的东西?有没有更好的方法可以做到这一点?

Could someone provide a reference as to why using the brackets with keyToGroupBy is working preferably in mdn?Is this considered a hack(works by chance) or it is something commonly used?is there a better way to do the same?

推荐答案

括号符号"不是方括号表示法.您在这里定义的是具有一个元素的数组的数组文字:

The "bracket notation" is not bracket notation. What you've defined there is an array literal for an array with one element:

let group = false;
let internalId = "someString";
let appliedTo = "someOtherString";
let keyToGroupBy = true === group ? internalId : appliedTo;

console.log(Array.isArray([keyToGroupBy]))

因此，它起作用"是因为对象的属性是字符串或符号.由于您没有提供符号，因此它将变成一个字符串.当您使用数组执行此操作时，结果是...一个等于第一个元素的字符串:

So, it "works" because the properties of objects are either strings or symbols. Since you're not supplying a Symbol, it's going to be turned into a string. And when you do that with an array, the result is...a string equal to the first element:

let group = false;
let internalId = "someString";
let appliedTo = "someOtherString";
let keyToGroupBy = true === group ? internalId : appliedTo;

let arr = [keyToGroupBy];

console.log(String(arr) === arr[0]);
console.log(String(arr));

将数组转换为字符串涉及内部调用 Array#join() ，并且由于没有其他值，因此不会产生分隔符，并且不会将任何内容添加到数组中的单个字符串.

Turning an array to a string involves internally calling Array#join() and since there are no other values, no separator would be produced and nothing will be added to the single string that is in the array.

因此，您正在采用一种相当round回的方式...只需检查字符串即可.

So, you're doing a rather roundabout way of...just checking for the string.

主要是黑客.它不是滥用类型转换规则，但肯定会绕过它们.

It's mostly a hack. It's not quite abusing the rules of type conversion but certainly skirting them.

不，不是.没有理由将字符串包装到数组中……然后如果您只需要一个字符串，则将其再次转换为字符串.

No, it's not. There is no reason to wrap strings into arrays...and then convert them to a string again if all you need is a string in the first place.

是的，只是在任何地方都没有数组文字:grouped.hasOwnProperty(keyToGroupBy)

Yes, simply don't have an array literal anywhere: grouped.hasOwnProperty(keyToGroupBy)

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