Javascript 正则表达式检查第一个字符是否为大写
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Regex to check if the first character is uppercase
提问by Sam
I'm trying to check that the first character of a username is capital, the following can be letters or numbers and at most 20 characters long. Can someone explain why my syntax is wrong?
我正在尝试检查用户名的第一个字符是否为大写，以下可以是字母或数字，最多 20 个字符长。有人可以解释为什么我的语法错误吗？
/^[A-z][a-z0-9_-]{3,19}$/
回答by BoltClock
Your first Z is not a capital Z.
你的第一个 Z 不是大写的 Z。
/^[A-Z][a-z0-9_-]{3,19}$/
回答by Mateen Ulhaq
Why can't you let the poor users pick their own usernames? What you should do is convert all caps to lowercase.
为什么不能让可怜的用户自己选择用户名？您应该做的是将所有大写字母转换为小写字母。
"User Name".toLowerCase();
But if you are truly evil, you should change that zto a Z:
但是，如果你是真正的邪恶的，你应该更改z为Z：
/^[A-Z][A-Za-z0-9_-]{3,19}$/
回答by BronzeByte
I would do it like this:
我会这样做：
var firstChar = strToCheck.substring(0, 1);
if (firstChar == firstChar.toUpperCase()) {
// it is capital :D
}
回答by Adam Rackis
Your first character needs to be A-Z, not A-z
你的第一个角色必须是A-Z，而不是A-z
So
所以
/^[A-z][a-z0-9_-]{3,19}$/
/^[A-z][a-z0-9_-]{3,19}$/
Should be
应该
/^[A-Z][a-z0-9_-]{3,19}$/
/^[A-Z][a-z0-9_-]{3,19}$/
回答by ipr101
You have a typo, the first z should be a capital -
你有一个错字，第一个 z 应该是一个大写 -
/^[A-Z][a-z0-9_-]{3,19}$/
