函数返回假甚至条件为真为什么？

Question

function checkform(for1)
{ 
   var result=checkform1(for1);
   alert(result);
}
function checkform1(form)
{
    var valid=false;
    var val1 = document.getElementById('security_code').value;
    $.get(url, function(data) {
        if(data.toString()==val1.toString())
        {
            var elem = document.getElementById("captchaerr");
            elem.style.visibility = 'hidden';
            valid=true;
        }
        else
        {
            var elem = document.getElementById("captchaerr");
            elem.style.visibility = 'visible';
            valid=false;
        }           
    }); 
    return valid;
}

result alert is always false even the condtion(data.toString()==val1.toString()) is true how the control passes in this. thnks..

Answer 1

By default $.get aka Ajax.get is asynchronous (it runs in the background). So your function "checkform1" is returning before the Ajax request finishes and sets the "valid" variable.

Answer 2

Don't use toString(), as string. toString() will return string . Just test data == val1 .

Answer 3

You are making a asynchronous call, so if you want to check for the result then you have to do this inside the callback

 function checkform1(form)
{
    var valid=false;
    var val1 = document.getElementById('security_code').value;
    $.get(url, function(data) {
        if(data.toString()==val1.toString())
        {
        var elem = document.getElementById("captchaerr");
        elem.style.visibility = 'hidden';
        valid=true;
        }
        else
        {
        var elem = document.getElementById("captchaerr");
        elem.style.visibility = 'visible';
        valid=false;
        }      
        //here you will get the valid and 
        //not outside...outside it will be always false.
    }); 

    //This line will be executed immediately after the previous line
    // and will not wait for the call to complete, so this needs to be done 
    // in the callback. 
    return valid;

}

Answer 4

If your 'get' ajax call is an async one, you can use a callback to get the result:

function checkform(for1)
{ 
   checkform1(for1, function(result) //provide the callback to the async function
   {
     alert(result); 
   });      
}
function checkform1(form, callback)
{
    var valid=false;
    var val1 = document.getElementById('security_code').value;
    $.get(url, function(data) 
    {
        if(data.toString()==val1.toString())
        {
            var elem = document.getElementById("captchaerr");
            elem.style.visibility = 'hidden';
            valid=true;
        }
        else
        {
            var elem = document.getElementById("captchaerr");
            elem.style.visibility = 'visible';
            valid=false;
        }           
        if(callback)
            callback(valid);// call the callback INSIDE of the complete callback of the 'get' jquery function
    }); 

}

Answer 5

Just before condition put alert on both values alert(val1 + '---' + data) and see if its exactly same .

Also trim them before comparing just in case it has some padding to it.