I have major error where I have this error message "Error Loading Page" appears when I click 'submit' button.

html code

<div data-role="collapsible">
     <h3>ENTER YOUR INFORMATION HERE FOR DELIVERY</h3>
     <form id="deliveryform">
        <p>
           <label for="name">Name</label>
           <input type="text" name="inputname" id="inputname" placeholder="Fullname" <br>
        </p>

        <p>
            <label for="phone">Phone Number</label>
            <input type="text" name="inputphonenumber" id="inputphonenumber" placeholder="011123456789" required>
            <span id="warning1"></span><br>
        </p>
                        
        <p>
            <label for="email">Email</label>
            <input type="text" name="inputemail" id="inputemail" required><br>
        </p>

            <fieldset>
                  <input type="submit" value="Submit" onclick="validation()"><br>
            </fieldset>        
     </form>
</div>

javascript

function validation()
{
    var a=document.getElementById("inputname").value;
    var b=document.getElementById("inputphonenumber").value;
    var c=document.getElementById("inputemail").value;
    var emailformat = "[a-z0-9._%+-]+@[a-z0-9.-]+\.[a-z]{2,}$";

    if(a=="")
    {
        alert("Please enter a name");
        return false;
    }

    if(isNaN(b))
    {
        document.getElementById("warning1").innerHTML="Please insert numbers Only!";
        return false;
    }

    if(!c.match(emailformat))
    {
        alert("Please use the correct format.Example : abc123@gmail.com");
        return false;
    }
    
    else
    alert("Submit successfully")
    return true;
}

How to solve this Error Loading Page error? I really need help with this. I don't really understand jquery codes, so I hope someone can explain it in javascript if possible.