Javascript verification email address

The email address has the following unifiedStandard Format: Username @ server domain name.

The user name indicates the user ID of the email address, registration name, or email recipient. The @ symbol is the domain name of the email server you are using. @ Can be read as "at", that is, ". The entire email address can be understood as the address of a user on a server on the network.
1. User Name, which can be selected by yourself. By letter ~ Z (Case Insensitive), numbers 0 ~ 9. It may consist of a dot, a minus sign, or an underscore. It can only start and end with a number or a letter, for example, beijing.2008. The username length is 4 ~ 18 characters.
2. It depends on the website you are using and represents the email service provider. For example, Netease has @ 163.com/@126.com/@188.com/@yeah.comand so on. The new wave is @ sina.com/@vip.sina.com.

 

Complete JS verification email
Function char_test (CHR)
// Character Detection Function
{
VaR I;
VaR smallch = "abcdefghijklmnopqrstuvwxyz ";
VaR bigch = "abcdefghijklmnopqrstuvwxyz ";
For (I = 0; I <26; I ++)
If (CHR = smallch. charat (I) | CHR = bigch. charat (I ))
Return (1 );
Return (0 );
}

Function spchar_test (CHR)
// Number and special character Detection Function
{
VaR I;
VaR spch = "_-. 0123456789 ";
For (I = 0; I <13; I ++)
If (CHR = spch. charat (I ))
Return (1 );
Return (0 );
}

Function email_test (STR)
{
VaR I, flag = 0;
VaR at_symbol = 0;
// "@" Detected location
VaR dot_symbol = 0;
// "." Detected location
If (char_test (Str. charat (0) = 0)
Return (1 );
// The first character must contain letters

For (I = 1; I <Str. length; I ++)
If (Str. charat (I) = '@')
{
At_symbol = I;
Break;
}
// Check the position @

If (at_symbol = Str. Length-1 | at_symbol = 0)
Return (2 );
// No email server Domain Name

If (at_symbol <3)
Return (3 );
// The account must contain less than three characters

If (at_symbol> 19)
Return (4 );
// The account contains more than 19 characters

For (I = 1; I <at_symbol; I ++)
If (char_test (Str. charat (I) = 0 & spchar_test (Str. charat (I) = 0)
Return (5 );
For (I = at_symbol + 1; I <Str. length; I ++)
If (char_test (Str. charat (I) = 0 & spchar_test (Str. charat (I) = 0)
Return (5 );
// Other special characters are not allowed

For (I = at_symbol + 1; I <Str. length; I ++)
If (Str. charat (I) = '.') dot_symbol = I;
For (I = at_symbol + 1; I <Str. length; I ++)
If (dot_symbol = 0 | dot_symbol = Str. Length-1)
// Check whether the server name is ".".
Return (6 );

Return (0 );
// The email name is valid.
}
Function emailcheck (STR ){
// Var ST = email_test (STR );
If (Str. Length = 0)
{Alert ("enter email ");}
Else
{
If (email_test (STR) = 1) Alert ("the first character of email must be a letter ");
If (email_test (STR) = 2) Alert ("No email server domain name ");
If (email_test (STR) = 3) Alert ("the email account contains less than three characters ");
If (email_test (STR) = 4) Alert ("the email account contains more than 19 characters ");
If (email_test (STR) = 5) Alert ("email cannot use other special characters ");
If (email_test (STR) = 6) Alert ("simply check whether there is". "To determine whether the server name is legal ");
}
}

 

<SCRIPT type = "text/JavaScript" Language = "JavaScript" src = "JS/function. js"> </SCRIPT>

Call <input name = "mail" type = "text" id = "mail" onblur = "emailcheck (this. Value)"/>