js simply implements the verification code of user registration information_javascript skills

//Check whether the input content is valid when the input box loses focus
function checkText(obj)
{
//Get the id value of the input box
var id= obj.name;
var text=document.getElementById(id.toString().toUpperCase()).value;

//Determine whether it is empty
if(text.replace(/s/g, "") ==="")
{
document.getElementById(id).innerHTML="Input cannot be empty";
}
else
{
//Assembly method
//Convert the first letter to uppercase, leaving the rest unchanged
var firstChar=id.charAt(0).toString().toUpperCase();
//
var strsub=id.substring(1, id.length);
var strMethod="check" firstChar strsub "()";
var isTrue = eval(strMethod);
if(isTrue)
{
document.getElementById( id).innerHTML="Input is valid";
}
}


}

function checkUsername()
{
//Simply determine the length of the username
var id = document.getElementById("USERNAME");
var username=id.value;
if(username.length > 10)
{
document.getElementById(id.name).innerHTML = "The entered username is too long";
return false;
}
else
return true;
}
function checkPassword()
{
var password = document.getElementById("PASSWORD").value;
return true;
}
function checkPassword2()
{
var id=document.getElementById("PASSWORD");
var id2=document.getElementById("PASSWORD2");
var password = id.value ;
var password2 = id2.value;
if(password!=password2)
{
document.getElementById(id.name).innerHTML="Password is inconsistent";
return false;
}
return true;
}
function checkIDNumber()
{
var id=document.getElementById("IDNUMBER");
var IDNumber =id.value;
if(IDNumber.length<18||IDNumber.length>19)
{
document.getElementById(id.name).innerHTML="The ID number length is wrong";
return false ;
}
var expr=/([0]{18}[x|y]?)|([1]{18}[x|y]?)/i;
if(expr .test(IDNumber))
{
document.getElementById(id.name).innerHTML="ID card number cannot be all '0' or all '1'";
return false;
}
return true;
}
function checkPhoneNumber()
{
// Use regular expressions to match input data
var id=document.getElementById("PHONENUMBER");
var phone = id.value;
//If a non-numeric character is matched, false will be returned
var expr = /D/i;
if(expr.test(phone))
{
document.getElementById(id.name).innerHTML="Cannot enter non-numeric characters";
return false;
}
return true;

}
function checkEmail()
{
// Use regular expressions to match input data
var id = document.getElementById("EMAIL")
var email = id.value;
// It starts with a letter or number, followed by @, and the letter or number ends with .com
var expr = /^([0-9]|[a-z]) @([0-9]|[a-z]) (.[ c][o][m])$/i;
if(!expr.test(email))
{
document.getElementById(id.name).innerHTML="The input email format is false";
return false;
}
return true;
}