JAVASCRIPT - 未捕获的类型错误：无法读取 null 的属性“值”
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/11928205/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
JAVASCRIPT - Uncaught TypeError: Cannot read property 'value' of null
提问by George Sumpster
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Javascript Form Testing</title>
</head>
<body>
Name: <input type="text" name="Name" value="Name" id="fname"> <br>
Email: <input type="text" name="Email" value="Email" id="mail" > <br>
Phone: <input type="text" name="Number" value="Phone Number" id="dvr" onchange="validatePhone();">
<span id="phoneval"> ?</span>
<script type="text/javascript">
phonenum = document.getElementById("dvr").value.length;
function validatePhone() {
if (phonenum == 10){
document.getElementById('phoneval').innerhtml="<-- Valid";
}
else{
document.getElementById('phoneval').innerhtml="<-- Not Valid";
}
}
</script>
</body>
</html>
Hi, I was getting the error 'Uncaught TypeError: Cannot read property 'value' of null' when the tag was in the head, but since I moved it, it went away. However, now it outputs no error and does NOTHING. Please help?
嗨，当标签位于头部时，我收到错误“未捕获的类型错误：无法读取 null 的属性‘值’”，但由于我移动了它，它消失了。但是，现在它没有输出错误并且什么也不做。请帮忙？
Sorry for any formatting and things, new :/
抱歉任何格式和事情，新的：/
回答by Adam Heath
Edit:
编辑：
Slightly different implementation that works: http://jsfiddle.net/SfTR2/Make sure the JS is loaded after the HTML, or use window.onload
稍微不同的实现：http: //jsfiddle.net/SfTR2/确保在 HTML 之后加载 JS，或者使用window.onload
Original answer:
原答案：
You need to get the length within the validation function:
您需要在验证函数中获取长度：
function validatePhone() {
var phonenum = document.getElementById("dvr").value.length; //MOVE IT HERE
if (phonenum == 10){
document.getElementById('phoneval').innerHTML="<-- Valid";
}
else{
document.getElementById('phoneval').innerHTML="<-- Not Valid";
}
}
As previously you were caching the empty length.
如前所述，您正在缓存空长度。
Also, as @su mentioned, you need to use innerHTML
另外，正如@su 提到的，您需要使用 innerHTML
回答by su-
add
添加
validatePhone();
to the end of the script (you defined the function but never called it). And change innerhtml to innerHTML
到脚本的末尾（您定义了函数但从未调用过它）。并将innerhtml更改为innerHTML
