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Editorial Team
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Asked: 2026-05-12T05:03:08+00:00

I have this code: <!DOCTYPE html PUBLIC -//W3C//DTD XHTML 1.0 Transitional//EN http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd> <html xmlns=http://www.w3.org/1999/xhtml

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I have this code: 

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
<head>
<title>sss</title>
<meta http-equiv="content-type" content="text/html; charset=utf-8" />


<script type='text/javascript'>
function isAlphabet(obj){

    var alphaExp = /[^a-z0-9_-]+/;
    if(!obj.value.match(alphaExp)){
        return true;
    }
    else{
        alert('the bad symbols');
        obj.focus();
        return false;
    }
}
</script>

</head>
<body>

    <form action="/">
        <input type='text' id='letters' onblur="isAlphabet(this)"/>
    </form>

</body>
</html>

And I want to show an Alert() displaying only those characters for which validation fails.

For example :

If an input contains symbols like ” #abc ” , the Alert Message should show only “#”. How can this be done?

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1 Answer

  1. Editorial Team

    Here’s a simple way to do it… it’s not be the most efficient though:

    function isAlphabet(obj)
{
    var val = obj.value;
    var alphaExp = /[^a-z0-9_-]+/;

    var valid = true;
    var badchars = "";

    for( a = 0; a < val.length; a++ )
    {
        if(val[a].match(alphaExp))
        {
            badchars += "," + val[a];
            valid = false;
        }
    }

    if( !valid )
    {
        alert("The following characters are not allowed: " + badchars.substr(1));
        obj.focus();
    }

    return valid;
}
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