Javascript按ID获取元素并设置值 [英] Javascript Get Element by Id and set the value
问题描述
我有一个javascript函数，我传递一个参数。该参数表示我的网页中元素（隐藏字段）的ID。我想更改此元素的值。
I have a javascript function to which I pass a parameter. The parameter represents the id of an element (a hidden field) in my web page. I want to change the value of this element.
function myFunc(variable){
var s= document.getElementById(variable);
s.value = 'New value'
}
当我这样做时，我收到一个错误，因为该对象为null，因此无法设置该值。但我知道该对象不是null，因为我在浏览器生成的html代码中看到它。
无论如何，我尝试了下面的代码来调试
When I do this, I get an error that the value cannot be set because the object is null. But I know the object is not null because I see it in the html code generated by the browser. Anyways, I tried the following code to debug
function myFunc(variable){
var x = variable;
var y = 'This-is-the-real-id'
alert(x + ', ' + y)
var s= document.getElementById(x);
s.value = 'New value'
}
当提醒信息时显示，两个参数都相同，但我仍然得到错误。但是当我做的时候一切正常
When the alert message shows up, both parameters are the same, but I still get the error. But everything works fine when I do
var s= document.getElementById('This-is-the-real-id');
s.value = 'New value'
我该怎样解决这个问题
编辑
我设置值的元素是隐藏字段，id是动态det，如页面负载。我试过在$（document）.ready函数中添加了这个但是没有工作
The element for which I am setting the value is hidden field and the id is det dynamically, as the page loads. I have tried added this in the $(document).ready function but did not work
推荐答案
如果执行了myFunc（变量）在将textarea呈现为页面之前，您将获得null异常错误。
If myFunc(variable) is executed before textarea is rendered to page, you will get the null exception error.
<html>
<head>
<title>index</title>
<script type="text/javascript">
function myFunc(variable){
var s = document.getElementById(variable);
s.value = "new value";
}
myFunc("id1");
</script>
</head>
<body>
<textarea id="id1"></textarea>
</body>
</html>
//Error message: Cannot set property 'value' of null
所以，请确保你的textarea确实存在于页面中，然后调用myFunc，你可以使用window.onload或$（document）.ready函数。
希望它有用。
So, make sure your textarea does exist in the page, and then call myFunc, you can use window.onload or $(document).ready function. Hope it's helpful.
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