querySelector和getElementById通过id获取元素的区别

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 "B\26 W\3F".