js querySelector和getElementById通过id获取元素的区别

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我是靠谱客的博主酷酷煎蛋，最近开发中收集的这篇文章主要介绍js querySelector和getElementById通过id获取元素的区别，觉得挺不错的，现在分享给大家，希望可以做个参考。

概述

这是sina同事xiaoniu发现的，如下

<!DOCTYPE html> 
<html> 
<head> 
<meta charset="utf-8"/> 
</head> 
<body> 
<div id="02E503E2A1C011CFC85B7B701A0677EC0900000000000001"></div> 
<script> 
var str = '02E503E2A1C011CFC85B7B701A0677EC0900000000000001'; 
function bySelector(id) { 
return document.querySelector('#'+id); 
} 
function byId(id) { 
return document.getElementById(id); 
} 

alert(bySelector(str)); 
alert(byId(str)); 
</script> 
</body> 
</html>

两个函数bySelector，byId分别通过querySelector和getElementById获取元素.

页面上有id为“02E503E2A1C011CFC85B7B701A0677EC0900000000000001”的元素。

结果：所有支持querySelector的浏览器中通过bySelector均获取不到（报错），但通过getElementById却可以获取。

开始怀疑是id的字符串太长的原因导致querySelector获取不到。真正原因却是querySelector按css规范实现，即css标识符也不能以数字开头。

W3 写道
In CSS, identifiers (including element names, classes, and IDs in selectors) can contain only the characters [a-zA-Z0-9] and ISO 10646 characters U+00A0 and higher, plus the hyphen (-) and the underscore (_); they cannot start with a digit, two hyphens, or a hyphen followed by a digit. Identifiers can also contain escaped characters and any ISO 10646 character as a numeric code (see next item). For instance, the identifier "B&W?" may be written as "B&W?" or "B26 W3F".