JS form Verification

<SCRIPT>function Checkform () {if(Checkusername () &&checkpass () &&checkbirth () &&Checkemail ()) {        return true; }Else{        return false; }}//user name non-null + length + legitimacy verificationfunction Checkusername () {varName =Document.myform.txtUser; if(name.value=="") {alert ("Please enter user name");        Name.focus (); return false; }    if(name.value.length<4|| Name.value.length> -) {alert ("the user name is entered in a length of 4-16 characters"); Name.Select(); return false; }     for(varI=0; i<name.value.length;i++)      {         varchartest=name.value.toLowerCase (). charAt (i); if( (! (chartest>='0'&& chartest<='9') && (!) ( chartest>='a'&& chartest<='Z')) && (chartest!='_') {alert ("The user name contains illegal characters and can only include letters, numbers, and underscores"); Name.Select(); return false; }      }      return true;}//password non-null + length + Password confirmation verificationfunction Checkpass () {varpass=Document.myform.txtPass; varrpass=Document.myform.txtRPass; if(pass.value=="") {alert ("The password cannot be empty");        Pass.focus (); return false; }if(pass.value.length<6|| Pass.value.length> -) {alert ("password length is 6-16 characters"); Pass.Select(); return false; }    if(rpass.value!=pass.value) {Alert ("Confirm password inconsistent with password input"); Rpass.Select(); return false; }    return true;}//Date of birth verificationfunction Checkbirth () {varBirth=Document.myform.txtBirth.value; if(birth=="") {alert ("please fill in the date of birth"); return false; }Else if(birth.length<Ten) {alert ("Birth date format error"); return false; }Else{    //intercept string to get date        varYear=birth.substring (0,4); varMonth=birth.substring (5,7); varDay=birth.substring (8, birth.length); if(Birth.charat (4)!="-"|| Birth.charat (7)!="-"){//determine if the date meets the formatting requirementsAlert"date of birth format Yyyy-mm-dd"); Document.myform.txtBirth.Select(); return false; }Else if(IsNaN (year) | | IsNaN (month) | |IsNaN (Day)) {Alert ("the date must be a number"); Document.myform.txtBirth.Select(); return false; }        varTime=NewDate (); if(Parseint (year,Ten) <1900|| parseint (Year,Ten) >time.getyear ()) {Alert ("date of birth range from 1900-"+time.getyear () +"years"); Document.myform.txtBirth.Select(); return false; }Else if(parseint (Month,Ten) <1|| parseint (Month,Ten) > A) {alert ("the month you entered is not between 1-12 months"); Document.myform.txtBirth.Select(); return false; }Else if(Parseint (Day,Ten) <1|| parseint (Day,Ten) > to) {alert ("the number of days you entered is not between 1-31"); Document.myform.txtBirth.Select(); return false; }    }    return true;}//Email Verificationfunction Checkemail () {varStremail=Document.myform.txtEmail; if(stremail.value.length==0) {alert ("e-mail cannot be empty!");        Stremail.focus (); return false; }     if(StrEmail.value.indexOf ("@",0)==-1) {alert ("e-mail format is incorrect \ n must contain the @ symbol! "); Stremail.Select(); return false; }     if(StrEmail.value.indexOf (".",0)==-1) {alert ("The e-mail format is incorrect \ n must contain a. symbol! "); Stremail.Select(); return false; }     return false;}</SCRIPT>

JS form Verification