JavaScript form letters validation function on name

I am just writing a JavaScript validation for my registration form, but I can't validate names by using str.match() or str.test() functions. I thought my code is corrent, but probably it is not. Can anyone check it please?

var nick = document.getElementById("nickid");
var name = document.getElementById("jmenoid");
var letters = /^[A-Za-z]+$/; 
 
if(nick){
    var kontrolaNicku = function(e){
        if (nick.value.length < 3){
            nick.className = "invalid invalidbox";
        }else if (letters.test(nick)== (false)){
            nick.className = "invalid invalidbox";
        }else{
            nick.className = "input";
        }     
    };
nick.addEventListener("blur", kontrolaNicku);
}

if(name){
    var kontrolName = function(e) {
        if ((name.value.match(letters) == null) || (name.value.length < 1)){
            nick.className = "invalid invalidbox";
        } else {
            nick.className = "input";
        }
    };
name.addEventListener("blur", kontrolName);    
}

Thanks for any answers.