Declare variable within Javascript functions

Question

I am new to Javascript. Recently I am trying to prepare a checkform function, although the function works, IE mentioned the "msg2" at the end was not declared, may experts please teach me how to make it work? Thanks a lot!

function check_si_form_info(form,mark,edit){
     if(mark==11 || mark=="all"){
            if(form.login.value==""){
                si_check_login.innerHTML="Please enter Login Name!";
                si_check_login.style.height="auto";
                form.login.style.backgroundColor="#FFD5FF";
                return false;
            }else if (form.login.value!==""){ 
            var loginname = form.login.value;
            xmlhttp=new XMLHttpRequest();
            xmlhttp.open('get','si/check_si_loginname.php?loginname='+loginname,true);
            xmlhttp.onreadystatechange = function(){
                if(xmlhttp.readyState == 4){
                    if(xmlhttp.status == 200){
                        msg2 = xmlhttp.responseText;
                        if(msg2 == '2'){
                        si_check_login.innerHTML="Login name is not available!";
                        si_check_login.style.height="auto";
                        form.login.style.backgroundColor="#FFD5FF";
                        return false;
                        }else if(msg2 == '1'){
                        si_check_login.innerHTML="";
                        si_check_login.style.height="0px";
                        form.login.style.backgroundColor="#FFFFFF";
                        }
                    }//200
                }//4            
            }//onreadystatechange
            xmlhttp.send(null);
            }
            if (msg2 == '2'){
            return false;
            }
    }//11
   }

Rob W · Accepted Answer · 2011-10-07T06:53:01.593

To declare a variable, add var msg2; at the beginning of your Currently, when your end of the function's body has reached, msg2 is not yet defined. Also, you should declare all variables (xmlhttp) using var, unless you want them to leak to the global scope.

A variable can be defined in some ways:

var msg2; inside the function: This DECLARES a private variable, and initialised it at undefined
var msg2; outside the function: Declares a variable. Private if the inner function is contained within another scope, eg function outer(){var msg2;function inner(){...}}. Public otherwise.
msg2=null; anywhere: This ASSIGNS null to variable msg2. If it has been defined already, see the previous line. Else, it will be publicly defined.

Consider your code:

function check_si_form_info(form,mark,edit){
     var msg2;// <-- Declare a variable
     if(mark==11 || mark=="all"){
            if(form.login.value==""){
               ...
                return false;
            }else if (form.login.value!==""){ 
            var loginname = form.login.value;
            xmlhttp=new XMLHttpRequest();
            xmlhttp.open('get','si/check_si_loginname.php?loginname='+loginname,true);
            xmlhttp.onreadystatechange = function(){
                if(xmlhttp.readyState == 4){
                    if(xmlhttp.status == 200){
                        msg2 = xmlhttp.responseText;
                        if(msg2 == '2'){
                            ...
                            form.login.style.backgroundColor="#FFD5FF";
                            return false; // <--- false isn't received by any func
                        }else if(msg2 == '1'){
                            ...
                        }
                    }//200
                }//4            
            }//onreadystatechange
            xmlhttp.send(null);
            }
            if (msg2 == '2'){ //<---This condition is always false
                return false;
            }

score 0 · Answer 2 · edited Mar 01 '15 at 15:09

0

declare the msg2 as a global variable then only you access it outside of the function.

put this line before the function

var msg2 ="";
function check_si_form_info(form,mark,edit){

edited Mar 01 '15 at 15:09

GitaarLAB

14,536
11
60
80

answered Oct 07 '11 at 06:47

balaphp

1,306
5
20
40

Declare variable within Javascript functions

2 Answers2