将事件侦听器添加到多个元素 [英] Adding event listeners to multiple elements

问题描述

我一直在努力解决这个问题好几个小时。

I've been struggling with this for a good couple of hours now.

我想为所有添加一个事件监听器<在页面上选择> ，到目前为止我已经得到了这段代码：

I want to add an event listener to all <select>s on a page and I've got this piece of code so far:

onload = function(e) {
    sels = document.getElementsByTagName('select');
    for(i=0; i<sels.length; i++) {
        sels[i].addEventListener('change', alert('test!'), false);
    }
}

这只会在页面加载时触发警报不是当我更改任何< select> s中的值时。

This only triggers the alert when the page is loaded and not when I change the value in any of my <select>s.

我可以轻轻一点正确的方向，好吗？ ： - ）

Can I get a nudge in the right direction, please? :-)

推荐答案

当你调用 alert（）时，你需要有匿名函数/ code>在你的例子中立即起作用：

You need to have there anonymous function for that as you invoke alert() function immediately in your example:

 ... .addEventListener('change', function() { alert('test!')}, false ...

现在根据您的代码 addEventListener 尝试添加 undefined 的结果（返回 alert（）函数）。

For now according to your code addEventListener tries to add result of undefined (return of alert() function).

或者你只需​​传递函数处理程序：

Or you can just pass function handler for that:

function alertMe() {
    alert( 'test!' );
}
...

... .addEventListener('change', alertMe, false ...

注意：通过使某些函数（arg [， arg ...]）调用引用不是函数，而是函数返回。

Note: that by making somefunction(arg[, arg...]) call you reference not to function, but to what function returns.

这篇关于将事件侦听器添加到多个元素的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！