professional_javascript_for_web/ch14/TextboxTabForwardExample01.htm

<!DOCTYPE html>
<html>
    <head>
        <title>Textbox Tab Forward Example</title>
        <script type="text/javascript" src="EventUtil.js"></script>
    </head>
    <body>
        <form method="post" action="http://www.nczonline.net">
            <p>Enter your telephone number:</p>
            <input type="text" name="tel1" id="txtTel1" size="3" maxlength="3" >
            <input type="text" name="tel2" id="txtTel2" size="3" maxlength="3" >
            <input type="text" name="tel3" id="txtTel3" size="4" maxlength="4" >

            <input type="submit" value="Submit">
        </form>
        <script type="text/javascript">
        (function(){
       
            function tabForward(event){            
                event = EventUtil.getEvent(event);
                var target = EventUtil.getTarget(event);
                
                if (target.value.length == target.maxLength){
                    var form = target.form;
                    
                    for (var i=0, len=form.elements.length; i < len; i++) {
                        if (form.elements[i] == target) {
                            if (form.elements[i+1]){
                                form.elements[i+1].focus();
                            }
                            return;
                        }
                    }
                }
            }
                        
            var textbox1 = document.getElementById("txtTel1"),
                textbox2 = document.getElementById("txtTel2"),
                textbox3 = document.getElementById("txtTel3");
            
            EventUtil.addHandler(textbox1, "keyup", tabForward);        
            EventUtil.addHandler(textbox2, "keyup", tabForward);        
            EventUtil.addHandler(textbox3, "keyup", tabForward);        
                
        })();
        </script>
    </body>
</html>