javascript 无法读取 null 的属性“innerHTML”
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Cannot read property 'innerHTML' of null
提问by Mr_Green
I am beginner in javascript.
我是 javascript 初学者。
js file
js文件
var msgErrorPalletizedWeight = document.getElementById('msgError');
function palletizedWeightValidation() {
console.log("hello");
/*ERROR*/ msgErrorPalletizedWeight.innerHTML += ("Please enter all the values marked with *");
}
HTML
HTML
<head runat="server">
<title></title>
<link href="Styles/Site.css" rel="stylesheet" type="text/css" />
<script src="Scripts/file.js" type="text/javascript"></script>
</head>
<body>
<p id="msgError"></p>
<asp:Button ID="btnSubmitPalletized" runat="server" Text="Submit"
OnClientClick="palletizedWeightValidation()" />
</body>
ERROR
错误
Cannot read property 'innerHTML' of null
无法读取 null 的属性“innerHTML”
I searched many sites before asking here, they all recommending to check for null before validations which I can do but my problem here is I want to add some text to the ptag as you can see.. How to achieve that? I even tried appending, thought it might solve the problem. I know this is a silly mistake because there are many posts on this... the thing is that I cant understand where I am going wrong.
我在问这里之前搜索了很多网站，他们都建议在验证之前检查空值，我可以这样做，但我的问题是我想在p标签中添加一些文本，如您所见..如何实现？我什至尝试附加，认为它可以解决问题。我知道这是一个愚蠢的错误，因为有很多关于这个的帖子......问题是我无法理解我哪里出错了。
Please help.
请帮忙。
回答by Adil
You are tryingto access the elementof html when it is not ready, put the statement in event function to get the element in function palletizedWeightValidation.
你trying要访问的elementhtml 当它不是时ready，将语句放在事件函数中以获取函数中的元素palletizedWeightValidation。
function palletizedWeightValidation() {
var msgErrorPalletizedWeight = document.getElementById('msgError');
console.log("hello");
/*ERROR*/ msgErrorPalletizedWeight.innerHTML += ("Please enter all the values marked ith *");
}
EDITTo stop postback, you need to return false from javascrip function.
编辑要停止回发，您需要从 javascript 函数返回 false。
<asp:Button ID="btnSubmitPalletized" runat="server" Text="Submit"
OnClientClick="return palletizedWeightValidation()" />
function palletizedWeightValidation() {
var msgErrorPalletizedWeight = document.getElementById('msgError');
console.log("hello");
/*ERROR*/ msgErrorPalletizedWeight.innerHTML += ("Please enter all the values marked ith *");
return false; // returning true will cause postback.
}
回答by Luka
The important thing is when your js file gets executed. If you load js file inside head tag, your file will be executed before DOM is created. That means, document.getElementById function returns null.
重要的是你的 js 文件何时被执行。如果你在 head 标签中加载 js 文件，你的文件将在创建 DOM 之前执行。这意味着，document.getElementById 函数返回 null。
回答by Justin McDonald
The error you are getting is caused because you are trying to read an attribute of a NULL object. This means that your line:
你得到的错误是因为你试图读取一个 NULL 对象的属性。这意味着您的线路：
var msgErrorPalletizedWeight = document.getElementById('msgError');
is not finding any elements on your page.
没有在您的页面上找到任何元素。
