javascript 无法读取 null 的属性“className”
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/26955805/
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
Cannot read property 'className' of null
提问by rbazzle
This isn't working. I have an element in my html with the id "color". What is the deal? I just want it to add to the class of that element.
这不起作用。我的 html 中有一个元素，ID 为“color”。交易是什么？我只是想让它添加到该元素的类中。
var el = document.getElementById("color");
var number = Math.floor((Math.random() * 5) + 1);
switch (number) {
case 1:
el.className += " blue";
break;
case 2:
el.className += " yellow";
break;
case 3:
el.className += " red";
break;
case 4:
el.className += " green";
break;
case 5:
el.className += " purple";
break;
}
回答by axelduch
I'd say this comes from the fact the body is not loaded when you try to get the #colorelement.
我会说这是因为当您尝试获取#color元素时没有加载正文。
Just wrap the thing inside this
把东西包在里面
window.onload = function () {
// your code
};
Or you can load your code at the end of the body
或者您可以在正文的末尾加载您的代码
<body>
<!-- you content -->
<script src="your-script.js"></script>
</body>
And finally you can listen for the DOMContentLoadedevent. It's a little faster than window.onload but has slightly less support, IE9+.
最后，您可以监听DOMContentLoaded事件。它比 window.onload 快一点，但对 IE9+ 的支持略少。
document.addEventListener("DOMContentLoaded", function(event) {
// your code
});
回答by rbazzle
I declared a variable "el" that wasn't within the scope of the switch.
我声明了一个不在 switch 范围内的变量“el”。
