Javascript RegEx没有像预期的那样返回false

Question

不是RegEx的大用户 - 从来没有真正理解它们！但是，我觉得检查用户名字段输入的最好方法是只允许字母（上或下），数字和_字符，并且必须按照站点策略以字母开头。我的RegEx和代码是这样的：

var theCheck = /[a-zA-Z]|\d|_$/g; 
alert(theCheck.test(theUsername)); 

尽管尝试各种组合，一切都返回“真实”。

任何人都可以帮忙吗？

Answer 1

你的正则表达式时说：“确实theUsername包含字母，数字或下划线结束”。

试试这个：

var theCheck = /^[a-z]([a-z_\d]*)$/i; // the "i" is "ignore case" 

这是说“theUsername以字母开头且只包含字母，数字或下划线”。

注：我不认为你需要在这里的“克”，这意味着“所有比赛”。我们只是想测试整个字符串。

Answer 2

使用此为您的正则表达式：

^[A-Za-z][a-zA-Z0-9_]*$ 

Answer 3

怎么是这样的：

^([a-zA-Z][a-zA-Z0-9_]{3,})$ 

要解释整个模式：

^ = Makes sure that the first pattern in brackets is at the beginning 
() = puts the entire pattern in a group in case you need to pull it out and not just validate 
a-zA-Z0-9_ = matches your character allowances 
$ = Makes sure that this must be the entire line 
{3,} = Makes sure there are a minimum of 3 characters. 
    You can add a number after the comma for a character limit max 
    You could also use a +, which would merely enforce at least one character match the second pattern. A * would not enforce any lengths