JAVASCRIPT-检查第一个字母是否为A-Z
我正在尝试编写一个代码来检查有效的用户名。我做错了什么?如果我输入用户名并以a-z开头,则表示该用户名无效。 此外,我不能使用正则表达式。JAVASCRIPT-检查第一个字母是否为A-Z,javascript,Javascript,我正在尝试编写一个代码来检查有效的用户名。我做错了什么?如果我输入用户名并以a-z开头,则表示该用户名无效。 此外,我不能使用正则表达式。 var BR = "<br />"; var username = ""; var letter1; var digit; letter1 = username.substr(0,1); username = prompt("Please enter a your username:"); //First letter begin with
var BR = "<br />";
var username = "";
var letter1;
var digit;
letter1 = username.substr(0,1);
username = prompt("Please enter a your username:");
//First letter begin with a letter
if (letter1 >= "a" && letter1 <= "z") {
document.write("The first character is valid." + BR);
}
else {
document.write("The first character is not valid." + BR);
}
var BR=“
”;
var username=“”;
var-1;
var数字;
letter1=用户名.substr(0,1);
用户名=提示(“请输入用户名:”);
//第一个字母以字母开头
如果(字母1>=“a”&&letter1检查此小提琴
var BR=“
”;
var username=“”;
var-1;
var数字;
letter1=用户名.substr(0,1);
用户名=提示(“请输入用户名:”);
//第一个字母以字母开头
var aCode='a'.charCodeAt(0);
var zCode='z'.charCodeAt(0);
如果(username.charCodeAt(0)>=aCode&&username.charCodeAt(0)put letter1=username.substr(1,2)语句在之后从第行读取用户名
用户名=提示(“请输入用户名:”)
提示显示用户名后,您应该获得用户名的第一个字母。切换“letter1=”和“username=”语句的顺序。将您的字母转换为ascii,然后按如下方式检查:
我还检查了大写字母:
Javascript
var BR = "<br />";
var username = "";
var digit;
username = prompt("Please enter a your username:");
var ascii = username.charCodeAt(0);
//First letter begin with a letter
if (ascii >= 97 && ascii <= 122 || ascii >= 65 && ascii <= 90) {
document.write("The first character is valid." + BR);
}
else {
document.write("The first character is not valid." + BR);
}
var BR=“
”;
var username=“”;
var数字;
用户名=提示(“请输入用户名:”);
var ascii=用户名.charCodeAt(0);
//第一个字母以字母开头
如果(ascii>=97&&ascii=65&&ascii,那么硬编码ascii字符代码是非常糟糕的样式。请执行类似于var aCode=“a”。charCodeAt(0);
var BR = "<br />";
var username = "";
var digit;
username = prompt("Please enter a your username:");
var ascii = username.charCodeAt(0);
//First letter begin with a letter
if (ascii >= 97 && ascii <= 122 || ascii >= 65 && ascii <= 90) {
document.write("The first character is valid." + BR);
}
else {
document.write("The first character is not valid." + BR);
}