clickToAddItems.js

function clearErrors() {    
    for (var loopCounter = 0; 
        loopCounter < document.forms["numberFun"].elements.length; 
        loopCounter++) {
        if (document.forms["numberFun"].elements[loopCounter]
           .parentElement.className.indexOf("has-") != -1) {
            
            document.forms["numberFun"].elements[loopCounter]
               .parentElement.className = "form-group";
        }
    }    
} 

function resetForm() {
    clearErrors();
    document.forms["numberFun"]["num1"].value = "";
    document.forms["numberFun"]["num2"].value = "";
    document.getElementById("results").style.display = "none";
    document.getElementById("submitButton").innerText = "Submit";
    document.forms["numberFun"]["num1"].focus();
}

function validateItems() {
    clearErrors();
    var num1 = document.forms["numberFun"]["num1"].value;
    var num2 = document.forms["numberFun"]["num2"].value;
    if (num1 == "" || isNaN(num1)) {
        alert("Num1 must be filled in with a number.");
        document.forms["numberFun"]["num1"]
           .parentElement.className = "form-group has-error";
        document.forms["numberFun"]["num1"].focus();
        return false;
    }
   if (num2 == "" || isNaN(num2)) {
       alert("Num2 must be filled in with a number.");
       document.forms["numberFun"]["num2"]
          .parentElement.className = "form-group has-error"
       document.forms["numberFun"]["num2"].focus();
       return false;
   }
   document.getElementById("results").style.display = "block";
   document.getElementById("submitButton").innerText = "Recalculate";
   document.getElementById("addResult").innerText = Number(num1) +
                                                     Number(num2);
   document.getElementById("subtractResult").innerText = num1 - num2;
   document.getElementById("multiplyResult").innerText = num1 * num2;
   document.getElementById("divideResult").innerText = num1 / num2;
   // We are returning false so that the form doesn't submit 
   // and so that we can see the results
   return false;
}