What you could do is, a validation of the values, for example:
if the value of the input of fullanme is greater than some value length and if the value of the input of address is greater than some value length then redirect to a new page, otherwise shows an error for the input.
// We access to the inputs by their id's
let fullname = document.getElementById("fullname");
let address = document.getElementById("address");
// Error messages
let errorElement = document.getElementById("name_error");
let errorElementAddress = document.getElementById("address_error");
// Form
let contactForm = document.getElementById("form");
// Event listener
contactForm.addEventListener("submit", function (e) {
let messageName = [];
let messageAddress = [];
if (fullname.value === "" || fullname.value === null) {
messageName.push("* This field is required");
}
if (address.value === "" || address.value === null) {
messageAddress.push("* This field is required");
}
// Statement to shows the errors
if (messageName.length || messageAddress.length > 0) {
e.preventDefault();
errorElement.innerText = messageName;
errorElementAddress.innerText = messageAddress;
}
// if the values length is filled and it's greater than 2 then redirect to this page
if (
(fullname.value.length > 2,
address.value.length > 2)
) {
e.preventDefault();
window.location.assign("https://www.google.com");
}
});.error {
color: #000;
}
.input-container {
display: flex;
flex-direction: column;
margin: 1rem auto;
}<html>
<body>
<form id="form" method="POST">
<div class="input-container">
<label>Full name:</label>
<input type="text" id="fullname" name="fullname">
<div class="error" id="name_error"></div>
</div>
<div class="input-container">
<label>Address:</label>
<input type="text" id="address" name="address">
<div class="error" id="address_error"></div>
</div>
<button type="submit" id="submit_button" value="Submit request" >Submit</button>
</form>
</body>
</html>