JavaScript 错误：未捕获的类型错误：无法读取未定义的属性“删除”
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JavaScript error: Uncaught TypeError: Cannot read property 'remove' of undefined
提问by Ronni
I have a script to remove uploaded files after Add to success, but I get this error on site when it loads.
我有一个脚本可以在添加成功后删除上传的文件，但是在加载时我在网站上收到此错误。
"Uncaught TypeError: Cannot read property 'remove' of undefined"
What's missing?
缺少了什么？
<script>
onload=function() {
document.querySelectorAll("li[id^='uploadNameSpan']")[0].remove();
}
</script>
采纳答案by nem035
Basically, your issue is that, at the time you call this code, you don't have any elements in the DOM corresponding to the query "li[id^='uploadNameSpan']". So querySelectorAllreturns an empty NodeListwhich has undefinedat the 0position (or any position for that matter).
基本上，您的问题是，在您调用此代码时，DOM 中没有与 query 对应的任何元素"li[id^='uploadNameSpan']"。所以querySelectorAll返回一个空的NodeList，它undefined在该0位置（或任何位置）。
Breakdown of what is happening:
正在发生的事情的细分：
var liElements = document.querySelectorAll("li[id^='uploadNameSpan']"); // this returns an empty NodeList
var nonExistentFirstElement = liElements[0]; // this is undefined, there's nothing at the first position
nonExistentFirstElement.remove(); // thus, this is an error since you're calling `undefined.remove()`
Depending on your use case, one thing you can do is have a check for the amount of items returned before trying to remove:
根据您的用例，您可以做的一件事是在尝试删除之前检查返回的项目数量：
var liElements = document.querySelectorAll("li[id^='uploadNameSpan']");
if (liElements.length > 0) {
liElements[0].remove();
}
In general, you have to make sure to have the element in the DOM at the time you are trying to remove it.
通常，您必须确保在尝试删除该元素时在 DOM 中有该元素。
