不能使用“下载"作为 javascript 中的函数名 [英] Can't use "download" as a function name in javascript

问题描述

这个小片段有问题:

<a href="#" onClick="javascript:download();">测试</a>

一旦我在 Chrome 14.0 中点击链接，我就会得到一个

未捕获的类型错误:字符串不是函数

在 Firefox 和 IE 中它工作得很好.我通过重命名函数解决了这个问题，但我仍然很好奇 Chrome 中的下载"是什么.据我所知，这不是保留关键字，那可能是什么?

解决方案

元素在 HTML5 中具有 download 属性，如此处，默认值为 ""(空字符串).

这意味着 download === this.download 在 onclick 处理程序中(this 是 onevent 属性)，因此元素的 download 属性优于 window 的 download 属性.

这个小提琴 列出了默认情况下存在的所有字符串属性.你可以看到 download 和 innerHTML 一样是一个属性，也失败 作为函数使用时完全相同的原因(即试图引用 window.innerHTML，而是执行 elem.innerHTML()).

正如评论中所说，使用 window 不会混淆属性/属性变量的计算结果.

---

这种作用域行为实际上似乎不是由 this 值引起的，而是由特定的作用域链"引起的.正在建设中.

根据 HTML5 规范:><块引用>

词法环境范围

让 Scope 成为 NewObjectEnvironment(元素的文档，全局环境) 的结果.

如果元素有表单所有者，让 Scope 成为 NewObjectEnvironment(元素的表单所有者，Scope) 的结果.

让 Scope 成为 NewObjectEnvironment(元素的对象，Scope) 的结果.

即发生的事情是作用域链是 window -><代码>文档 ->element(增加优势).这意味着 download 的计算结果为 element.download 而不是 window.download.由此还可以得出的结论是，getElementById 会冒泡到 document.getElementById(假设 elem.getElementById 不存在).>

我设置了一个系统示例，以便您可以看到变量如何在范围内冒泡链:

window.a = 1;文件.a = 2;elem.a = 3;窗口.b = 4;文件.b = 5;窗口.c = 6;

然后， 记录 3, 5, 6 点击时.

I've had a problem with this little snippet:

<script>
function download() {
    alert('Hi');
}
</script>
<a href="#" onClick="javascript:download();">Test</a>

Once I click on the link in Chrome 14.0, I get a

Uncaught TypeError: string is not a function

in Firefox and IE it works just fine. I solved the problem by renaming the function but I'm still curious what's with the "download" thing in Chrome. It's not a reserved keyword as far as I know so what might it be?

解决方案

<a> elements have a download attribute in HTML5 as explained here, with a default value of "" (an empty string).

This means that download === this.download in the onclick handler (this is the element in onevent attributes), and therefore the download attribute of the element is superior to the download property of window.

This fiddle lists all string attributes that are present by default. You can see download is an attribute just like innerHTML, which also fails with the exact same reason when used as a function (i.e. trying to refer to window.innerHTML, but instead executing elem.innerHTML()).

As said in the comments, using window makes for no confusion as to what property/attribute variables will evaluate to.

---

This scope behaviour does actually not seem to due to the this value but rather a specific "scope chain" that is being constructed.

As per the HTML5 specification:

Lexical Environment Scope

Let Scope be the result of NewObjectEnvironment(the element's Document, the global environment).

If the element has a form owner, let Scope be the result of NewObjectEnvironment(the element's form owner, Scope).

Let Scope be the result of NewObjectEnvironment(the element's object, Scope).

I.e. what is happening is the scope chain is window -> document -> element (increasing superiority). This means that download evaluates to element.download and not window.download. What also can be concluded from this is that getElementById will bubble up to document.getElementById (given elem.getElementById does not exist).

I set up a systematic example so that you can see how variables bubble up the scope chain:

window.a   = 1;
document.a = 2;
elem.a     = 3;

window.b   = 4;
document.b = 5;

window.c   = 6;

Then, <a ... onclick="console.log(a, b, c)"> logs 3, 5, 6 when clicked.

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