JavaScript 如何识别事件对象变量?

2022-01-15 00:00:00 parameter-passing event-handling javascript dom-events

关于 JavaScript 事件对象的快速问题 - JavaScript 如何知道我何时尝试将事件变量传递给函数?例如，当我像这样定义 onclick 处理程序时:

Quick question about JavaScript event objects - how does JavaScript know when I'm trying to pass an event variable to a function? For example, when I define an onclick handler like so:

<button onclick='SendMessage(event)'></button>

JavaScript 是否仅仅因为我将它命名为事件"而传递事件变量?如果是这样，它为传递事件变量保留了哪些其他变量名称?(例如?ev?等等.)

Does JavaScript pass the event variable just because I named it "event"? If so, what other variable names does it reserve for the purpose of passing event variables? (e? ev? etc..)

如果是这种情况，是否可以通过命名局部或全局变量event"、e"等来覆盖它们?

If this is the case, can they be covered by naming local or global variables "event", "e", etc.. ?

推荐答案

它必须在内联事件中调用event.event 是 not 关键字，是 not JavaScript 中的保留字；它只是早期 Netscape 工程师决定的变量名称.

It must be called event in an inline event. event is not a keyword and is not a reserved word in JavaScript; it is merely the variable name the early Netscape engineers decided upon.

为事件提供的内联文本被有效地包装 1为:

The inline text supplied for the event is effectively wrapped 1 as:

function (event) {
   // the inline code
}

IE 使用 window.event 属性来传递事件信息，但名称一致，因此使用 event 将酌情回退到正常的 JavaScript 变量解析.

IE uses the window.event property to pass event information, but the names coincide so using event will fallback through the normal JavaScript variable resolution as appropriate.

当然，如果直接附加一个函数对象，那么事件变量，因为它只是第一个参数，可以任意命名.不幸的是，IE 的 window.event 方法必须是也处理了，调用参数 event 并没有解决它.

Of course, if attaching a function object directly then the event variable, because it's just the first parameter, can be named whatever is desired. Unfortunately IE's window.event approach must be dealt with as well, and calling the argument event doesn't address it.

elm.onclick = function (my_event_name) {
    my_event_name ||= window.event // for IE
    ...
}

(我建议尽可能避免内联事件，并使用统一/简化事件的库.)

(I would recommend avoiding inline events as much as possible and using a library that unifies/simplifies events.)

编码愉快！

1 HTML 中详细介绍了此行为5:Event Handlers，事件处理内容属性:

[内联事件，例如 onclick, text] 必须包含有效的 JavaScript 代码，该代码在解析时将匹配 [a function] 生产..

[inline event, e.g onclick, text] must contain valid JavaScript code which, when parsed, would match [a function] production ..

使用上面创建的脚本执行环境，创建一个函数对象..让函数有一个单独的参数称为事件.

Using the script execution environment created above, create a function object .. Let the function have a single argument called event.

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