(function(window, document, undefined) {
// code that should be taken care of right away
window.onload = init;
function init(){
// the code to be called when the dom has loaded
// #document has its nodes
}
})(window, document, undefined);
Also be careful how you execute the js on the page. For example if you do something like this:
This will return null because you'd be calling the document before it was loaded.
Use window.onload to wait for the dom nodes to load:
(function(window, document, undefined) {
// code that should be taken care of right away
window.onload = init;
function init(){
// the code to be called when the dom has loaded
// #document has its nodes
}
})(window, document, undefined);
我怀疑您使用相同的 ID 两次或更多次：在这种情况下 document.getElementById 应该至少返回第一个元素
There could be many reason why document.getElementById doesn't work
You have an invalid ID
ID and NAME tokens must begin with a letter ([A-Za-z]) and may be followed by any number of letters, digits ([0-9]), hyphens ("-"), underscores ("_"), colons (":"), and periods ("."). (resource: What are valid values for the id attribute in HTML?)
you used some id that you already used as <meta> name in your header (e.g. copyright, author... ) it looks weird but happened to me: if your 're using IE take a look at (resource: http://www.phpied.com/getelementbyid-description-in-ie/)
you're targeting an element inside a frame or iframe. In this case if the iframe loads a page within the same domain of the parent you should target the contentdocument before looking for the element (resource: Calling a specific id inside a frame)
you're simply looking to an element when the node is not effectively loaded in the DOM, or maybe it's a simple misspelling
I doubt you used same ID twice or more: in that case document.getElementById should return at least the first element
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评论（3）
还要注意页面上js的执行方式。例如，如果您执行以下操作：
这将返回 null，因为您将在加载文档之前调用该文档。
使用
window.onload等待 dom 节点加载：Also be careful how you execute the js on the page. For example if you do something like this:
This will return null because you'd be calling the document before it was loaded.
Use
window.onloadto wait for the dom nodes to load:它可能是由以下原因引起的：
请发布您的代码。
It can be caused by:
Please, post your code.
document.getElementById不起作用的原因可能有很多您的 ID 无效
<块引用>
ID 和 NAME 标记必须以字母 ([A-Za-z]) 开头，后面可以跟任意数量的字母、数字 ([0-9])、连字符 ("-")、下划线 (" _”）、冒号（“:”）和句点（“.”）。
（资源：什么是 id 属性的有效值HTML？)
你使用了一些已经在标题中用作
名称的 id（例如版权、作者...），它看起来很奇怪，但发生在我身上: 如果你是用IE看一下（资源：http://www.phpied.com/getelementbyid-description-in-ie /)
您正在定位框架或 iframe 内的元素。在这种情况下，如果 iframe 加载父级同一域内的页面，您应该在查找元素之前定位
contentdocument（资源：在框架内调用特定id )
当节点没有有效地加载到 DOM 中时，您只是在查找一个元素，或者可能是一个简单的拼写错误
我怀疑您使用相同的 ID 两次或更多次：在这种情况下
document.getElementById应该至少返回第一个元素There could be many reason why
document.getElementByIddoesn't workYou have an invalid ID
you used some id that you already used as
<meta>name in your header (e.g. copyright, author... ) it looks weird but happened to me: if your 're using IE take a look at(resource: http://www.phpied.com/getelementbyid-description-in-ie/)
you're targeting an element inside a frame or iframe. In this case if the iframe loads a page within the same domain of the parent you should target the
contentdocumentbefore looking for the element(resource: Calling a specific id inside a frame)
you're simply looking to an element when the node is not effectively loaded in the DOM, or maybe it's a simple misspelling
I doubt you used same ID twice or more: in that case
document.getElementByIdshould return at least the first element