document.getElementById返回null

Question

I'm trying to write an extension for Chrome at the moment. 我目前正在尝试为Chrome开发扩展程序。

What I'm trying to do right now is create an HTML form that has a button on it which, when pressed, shows a message box. 我现在想做的是创建一个HTML表单，上面带有一个按钮，当按下该按钮时，它将显示一个消息框。

My project consists of an HTML file and a JavaScript file. 我的项目包含一个HTML文件和一个JavaScript文件。

<html>
<head>
<style>
body {
  width:100px;
  font-family: sans-serif;
  font-size: 0.8em;
}
</style>
<script src="popup.js"></script>
</head>
<body>
<input id="buttonid" type="button" value="try it"></input>
</body>



chrome.tabs.onCreated.addListener(onCreated());

function myFunction()
{
alert("Hello World!");
}

function onCreated()
{
    var fld = document.getElementById("buttonid");
    if(fld==null)
    {
        alert("null");
    }
    else
    {
        alert("not null");
    }   
}

So my understanding is, when the HTML is rendered it runs my onCreated() function. 所以我的理解是，当呈现HTML时，它将运行我的onCreated（）函数。 This then looks for an element with ID="buttonid". 然后，它将查找ID =“ buttonid”的元素。 But it is ALWAYS returning null, so a message box comes up saying "null". 但这总是返回null，因此出现一个消息框，显示“ null”。

Can anyone explain this? 谁能解释一下？ This seems to make no sense. 这似乎没有任何意义。 I have tried running a slightly adapted version in IE but with identical results. 我尝试在IE中运行经过稍微调整的版本，但结果相同。

Just to be clear, I know this won't fulfil my description above but I am trying to access the button from the JavaScript before I attach an event to it. 只是要清楚一点，我知道上面的描述不符合我的描述，但是我尝试在将事件附加到JavaScript之前从JavaScript访问该按钮。

Answer 1

Replace 更换

chrome.tabs.onCreated.addListener(onCreated());

with 同

chrome.tabs.onCreated.addListener(onCreated);

Event handler rule #1: No parentheses! 事件处理程序规则1：不加括号！ - you do not want to execute the function, but register it. -您不想执行该功能，但要注册它。

Answer 2

Fixed! 固定！ I placed window.onload=function(){onCreated()}; 我放置了window.onload = function（）{onCreated（）}; on the first line. 在第一行。 This means that when the html is loaded it runs my function "onCreated"... Thanks guys, you pushed me in the right direction. 这意味着在加载html时它将运行我的函数“ onCreated” ...谢谢大家，您向正确的方向推了我。

document.getElementById返回null

问题描述

2 个解决方案

解决方案1
5 2013-01-22 22:01:35

解决方案2
0 2013-01-23 17:13:01

document.getElementById返回null

问题描述

2 个解决方案

解决方案1 5 2013-01-22 22:01:35

解决方案2 0 2013-01-23 17:13:01

解决方案1
5 2013-01-22 22:01:35

解决方案2
0 2013-01-23 17:13:01