javascript-检查用户名的第一个字符

Question

English isn't my primary language,so I'll try to do my best to explain myself...I need to, using javascript, check the first letter of input username of the user,and see if it's between AZ or az . If not it will delete the string the the user entered. Why isn't the code working?

function UsernameRegisterVaildation()
{
    var username = document.getElementById("usernameRegister");
    var x = false;
    var y = false;
    if (x.CharAt(0) >= 'A' && x.CharAt(0) <= 'Z')
        x = true;

    if (y.CharAt(0) >= 'a' && y.CharAt(0) <= 'z')
        y = true;

    if (!x || !y)
    {
        alert("WRONG USERNAME");
    }
}

and here's the input:

        Username: <input type="text" id="usernameRegister" name="UserNameRegister" onchange="UsernameRegisterVaildation();"/>

Answer 1

It's charAt , not CharAt . Also, you've got a reference to the element that holds the username, not the username itself - get the value property.

You may as well just use one regular expression, though:

if(!/^[a-z]/i.test(username.value)) {
    ...
}