HTML Form Onsubmit validation doesn't working for JS function

Question

I am trying to raise an error for a form if the fields are not numeric however it isn't raising any error and directing to the page I defined as action.

I tried to raise error with a function just alerts but it again didn't raise any error and opened the other jsp.

Below is inside head tags

<script type="text/javascript">
  function validation() {
    var a = document.getElementByid("a");
    var b = document.getElementByid("b");
    var c = document.getElementByid("c");
    var d = document.getElementByid("a").value;
    var e = document.getElementByid("b").value;
    var valid = true;
    if (a.value.length <= 0 || b.value.length <= 0) {
      alert("Lutfen alani bos birakmayiniz");
      valid = false;
    } else {
      if (isNan(d)) || isNan(e)) {
      alert("Rakam girmediniz. Rakam giriniz lütfen")
      valid = false;
    } else
      return valid;
  }
  }
</script>

Following is inside body tag

<form onsubmit="return validation();" method="get" action="response.jsp">
  </br>aaa <input type="text" id="a" value="0" />
  </br>bbb <input type="text" id="b" value="0" />
  </br>ccc <input type="text" id="c" />
  <input type="submit" value="Submit" />
</form>

I am sure that it could work even if js function is in head and form is in body.

Answer 1

There are multiple errors in your script code, change document.getElementByid to document.getElementById change isNan to isNaN and remove extra bracket at if(isNaN(d) ) use the below one

  <script type ="text/javascript">
            function validation()
            {
                var a = document.getElementById("a");
                var b = document.getElementById("b");
                var c = document.getElementById("c");
                var d = document.getElementById("a").value;
                var e = document.getElementById("b").value;
                var valid =true;
                if (a.value.length<=0 || b.value.length<=0)
                {
                    alert("Lutfen alani bos birakmayiniz");
                    valid =false;
                }
                else 
                {
                    if (isNaN(d) || isNaN(e))
                    {
                        alert("Rakam girmediniz. Rakam giriniz lütfen")
                        valid =false;
                    }


                }
                    return valid;

            }
        </script>