如果有的话，为什么 addEventListener 在事件之前触发? [英] Why does addEventListener fire before the event if at all?

问题描述

我正在 [在 jsfiddle 中] 尝试使用创建的函数将新创建的 TextNode 附加到以下 HTML 中的 <p>:

I was experimenting [in jsfiddle] w/a function created to append a newly created TextNode to the <p> in the HTML below:

    <button onclick="addTextNode('YES! ');">YES!</button>
    <button onclick="addTextNode('NO! ');">NO!</button>
    <button onclick="addTextNode('WE CAN! ');">WE CAN!</button>
    <hr />
    <p id="p1">First line of paragraph.</p>

这也是我的 javascript:

Here is my javascript as well:

    function addTextNode(text) {
        var newtext = document.createTextNode(text),
            p1 = document.getElementById("p1");

        p1.appendChild(newtext);
    }

这很好用.但是，当我试图通过从标记中删除行为来使我的 javascript不显眼"时，症结就会显现出来......

This works fine. However, the crux reveals itself when I attempt to make my javascript 'unobtrusive' by removing the behavior from the markup...

    <button>YES!</button>
    <button>NO!</button>
    <button>WE CAN!</button>
    <hr />
    <p id="p1">First line of paragraph.</p>

然后利用循环将 addEventListener 附加到每个 元素，然后使用子 TextNode 调用 addTextNode:

then utilizing a loop to attach addEventListener to each <button> element, which in turn uses the child TextNode to call addTextNode:

    function addTextNode(text) {
        var newtext = document.createTextNode(text),
            p1 = document.getElementById("p1");

        p1.appendChild(newtext);
    }

    var btns = document.getElementsByTagName("button");

    for(i = 0; i < btns.length; i++){
        var button = btns[i]; 
        button.addEventListener("click", addTextNode(button.innerHTML));
    }

我的代码发生了两件奇怪的事情:
当 [jsfiddle's] Code Wrap 设置为 'no wrap -在头脑中，什么都没有发生.

Two strange things happen with my code:
When [jsfiddle's] Code Wrap is set to 'no wrap - in head', nothing happens.

但是，当 Code Wrap 设置为 'onLoad'、'onDomReady' 或 'no wrap - in body' 函数在点击之前运行，我得到 this.

However, When Code Wrap is set to 'onLoad', 'onDomReady' or 'no wrap - in body' the function runs before the click and I get this.

谁能告诉我我错过了什么?

Could someone tell me what I'm missing?

推荐答案

你的问题的根源在这里:

The root of your problem is here:

button.addEventListener("click", addTextNode(button.innerHTML))

您正在执行该函数，而不是将其传递给事件侦听器.相反，通过引用传递函数，然后获取函数内部的 innerHTML.

You're executing the function rather than passing it to the event listener. Instead, pass the function by reference, then get the innerHTML inside the function.

function addTextNode() {
    var newtext = document.createTextNode(this.innerHTML),
        p1 = document.getElementById("p1");

    p1.appendChild(newtext);
}

var btns = document.getElementsByTagName("button");

for(i = 0; i < btns.length; i++){
    var button = btns[i]; 
    button.addEventListener("click", addTextNode);
}

http://jsfiddle.net/bn85J/

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