Question

javascript正则表达式判断用户名，字母数字

Answer 1

<input type="text" id="username" name="username" onchange="/^[\da-zA-Z]+$/.test(this.value) || alert('用户名有非法字符!');" />

Answer 2

(@"^[a-zA-Z][a-zA-Z0-9|_]{2,19}$"