{ In Scope }

Better Form Submissions with Event.preventDefault() and HTMLFormElement.reset()

January 04, 2019

Two tools to keep in your tool belt when adding forms to your website should be:

  1. Event.preventDefault()
  2. HTMLFormElement.reset()

The reason is that by default, on submission of a form, the page will redirect and refresh. The biggest reason that this becomes a problem is that if you wanted to do anything with that information later on, you can’t. The assumption is that the form data is sent off and there is no reason to keep it on the client side after submission.

That may have been true(r) in the past, but as we move toward more and more client-side work, we don’t want to lose our user data to a refresh.

That’s where Event.preventDefault() comes in handy. The HTMLFormElement.reset() is much more of a user experience feature in this context. Because we’re not navigating to a new site or refreshing, if we don’t use .reset() the user is likely to wonder whether or not anything actually happened.

Example Time!

Let’s imagine a basic form. It has one field to submit the customer’s name. In basic HTML, this form might look something like this.

<div>
  <form class="form-class">
    <input type="text" name="customer" placeholder="Your Name" required>
    <input type="submit">
  </form>
</div>

Adding A Basic Event Handler

Before we can see the value of the preventDefault() and reset() methods, we need to add a basic eventHandler. Imagine the following in a <script> tag for the HTML above.

// Create a variable that selects the form
let formClass = document.querySelector('.form-class')

// Define what happens on form submission
function submitForm(event) {
	console.log(`Form submitted!`);
	// The name the user types into the form.
	const name = document.querySelector('[name]').value;
  console.log(`The name is --> `, name);
}

// Add the event listner to the form
formClass.addEventListener('submit', submitForm);

If we were to open our page now and run our page, on submission, we’d likely see something like the following in our console.

console log of default form submission
The default form submission

Notice that after we submitted the form, we navigated to a new path, and now included more information (?customer=Stephen)

Use preventDefault() To Stop Sending Data / Redirecting

But unless you’re storing that form data somewhere, that redirection means that it’s lost to the ether.

Before we can prevent the redirect, we need a way to see it.

Adding console.log("The path is --> ", window.location.pathname); to the Javascript on the page will shine a light.

console log of default form submission with path logging
The default form submission with path logging

But, now we actually want to prevent the redirect so that we maintain access to the information. We can do this by adding one line to our submitForm method.

function submitForm (event) {
  event.preventDefault(); // <-- This is the money line
  console.log(`Form submitted!`);
  const name = document.querySelector('[name]').value;
  console.log(`The name is --> `, name);
}

Now, even though the form is submitted, we do not redirect.

console log of form submission prevented from redirect

Woot! Okay, step one down. But, you may have noticed that the name you entered is still hanging out. Though the form was submitted, since the page wasn’t refreshed, the user’s entry is still there.

After submission, the form data is still visible

Use HTMLFormElement.reset() To Clear A Form

Though, it’s likely the case that HTMLFormElement.reset() was envisioned to be used more in cases where a user wants to start over, the method works well in our case by clearing all user entries from the form post submission since we prevented the default behavior.

Reminder: The default behavior we prevented is tied to the submit event emitted by the form.

To modify our event handler to clear the entries after we’ve done what we needed to do, use the .reset() method on the form.

function submitForm (event) {
  event.preventDefault();
  console.log(`Form submitted!`);
  const name = document.querySelector('[name]').value;
  console.log(`The name is --> `, name);
  // Do anything else you want here
  formClass.reset(); // <-- Our *new* money line
}

The formClass variable is an HTMLFormElement and therefore has access to the reset method.

console log of formClass

However, this could just as easily be written as

function submitForm (event) {
  event.preventDefault();
  console.log(`Form submitted!`);
  const name = document.querySelector('[name]').value;
  console.log(`The name is --> `, name);
  // Do anything else you want here
  this.reset(); // <-- Our *new* money line
}

The reason this works, is because of the context in which the submitForm is invoked.

Recall, it was from an event listener that was attached to the formClass. If you look “to the left of the call-time dot” you’ll see that the context in which the submitForm function is run is the form.

Personally, I prefer to be explicit wherever possible, however, it is worth understanding how it works so that you can read someone else’s code if they do not have the same behaviors.

Video Walkthrough

I put together this video walkthrough to demonstrate all of these details live.

Further Reading

The HTMLFormElement has only three methods by default. The others are reportValidity() and submit(). There are, however, many events. Read more on MDN.

The preventDefault() method has no effect on non-cancelable events. But you can learn more about the nuances on MDN.

Thanks to Wes Bos and his JavaScript 30 Course for the inspiration to learn more about these methods.

<div>
  <form class="form-class">
    <input type="text" name="customer" autocomplete="off" placeholder="Your Name" required>
    <input type="submit">
  </form>
</div>

<script>
  console.log(`The path is --> `, window.location.pathname);
  let formClass = document.querySelector('.form-class');
  function submitForm (event) {
    event.preventDefault();
    console.log(`Form submitted!`);
    const name = document.querySelector('[name]').value;
    console.log(`The name is --> `, name);
    // Do anything else you want here
    formClass.reset();
  }
  formClass.addEventListener('submit', submitForm);
</script>

Stephen Weiss

Written by Stephen Weiss who lives in Chicago with his wife, Kate, and dog, Finn. Follow him on Twitter!