javascript - 非属性赋值变量是可删除的

Question

我正在阅读 this article在 Javascript delete 方法上，并尝试了这段代码:

function f(){
    var x = "abcd";
    console.log(delete x); //returns false, because x has DontDelete attribute
    y = "abcd";
    console.log(delete y); //returns true, but I didn't explicitly assign y as a property
}

这很奇怪，因为我没有为 y 使用属性赋值(如:window.y="abcd";)，文章 claims是如何让属性deleteable。

为什么 y 没有 DontDelete 属性？

更新:

在下面的答案中，声称 y 是可删除的，仅仅是因为它是 window 对象的属性。那不是真的。考虑以下代码段:

function f() {
    var functionx = "abcd";
    console.log(delete functionx); //returns false, because x has DontDelete attribute
    functiony = "abcd";
    console.log(delete functiony); //returns true, but I didn't explicitly assign functiony as a property to the window
}

//take 1
var globalx = "abcd";
console.log(this.globalx);//to prove x is a property of the global
console.log(delete globalx);//fails, even though x is a property of the window

//take 2
this.globaly = "abcd";
console.log(this.globaly);//to prove y is a property of the global
console.log(delete globaly);//succeeds, because I used property assignment

f();

在take 1中，globalx是window的一个属性，但是还是不可删除的。 delete 是否成功的标准不是变量是否是某物的属性(这始终为真)，而是该属性是否具有 DontDelete 属性集。

Answer 1

delete x 无效，因为它未解析为任何对象属性。

y 解析为 window 对象的属性。

https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Operators/delete :

delete expression

where expression should evaluate to a property reference