javascript 无法将事件传递给 addEventListener：关闭问题
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Can't pass event to addEventListener: closure issue
提问by EML
This one's driving me crazy... I have a loop which adds an event listener to an SVG object. The object is, for the sake of argument, a small circle, and I have to add mouseover and mouseout events for each of the 10 circles.
这个让我发疯了......我有一个循环，它向一个 SVG 对象添加了一个事件监听器。为了便于论证，对象是一个小圆圈，我必须为 10 个圆圈中的每一个添加 mouseover 和 mouseout 事件。
My first problem is the standard closure-scope thing - because all the listeners are added in the same loop, they all see the same invalid value of the loop variable. I can fix this, I think, but the second problem is that I have to pass 'event' to the listeners, and I can't find any way to fix both these issues simultaneously.
我的第一个问题是标准的闭包作用域——因为所有的监听器都被添加到同一个循环中，它们都看到循环变量的相同无效值。我想我可以解决这个问题，但第二个问题是我必须将“事件”传递给侦听器，我找不到同时解决这两个问题的任何方法。
I've tried various versions of this:
我已经尝试了这个的各种版本：
for(month = 0; month < nMonths; month++) {
...
shape.addEventListener(
"mouseover",
(function(event, index) { popup_on(event, foo, index); })(event, month),
false);
group.appendChild(shape);
}
This particular version gives me 'event is not defined'. popup_onis the real handler, and must get eventand the current value of month. Any idea how I should be doing this? Thanks.
这个特定版本给了我'事件未定义'。popup_on是真正的处理程序，必须获取event和 的当前值month。知道我应该怎么做吗？谢谢。
回答by Adam Rackis
The event will be passed to your function automatically—just make it the first argument to the function you pass to addEventListener. Also, false is the default value for the capture parameter.
该事件将被传递给你的函数自动-只是将其作为第一个参数传递给函数addEventListener。此外，false 是捕获参数的默认值。
(function() {
var i = month;
shape.addEventListener("mouseover", function(e) { popup_on(e, foo, i); });
})();
Also, are you ok with foobeing closed over in your event callback? If not, you could do the same thing with it
另外，您可以foo在事件回调中关闭吗？如果没有，你可以用它做同样的事情
(function() {
var i = month;
var f = foo;
shape.addEventListener("mouseover", function(e) { popup_on(e, f, i); });
})();
And if all these local variables are getting annoying, you can make them parameters to possibly make things a bit more tidy
如果所有这些局部变量都变得烦人，您可以将它们设置为参数以使事情更整洁
(function(i, f) {
shape.addEventListener("mouseover", function(e) { popup_on(e, f, i); });
})(month, foo);
