requestSubmit offers a way to validate a form before submit (#tilPost)

HTML form elements are the foundation for the interactions in web pages. And they improved quite a little bit over the last years. Today, developers can use different types (number, tel, color, …) and set different input modes (te…

HTML form elements are the foundation for the interactions in web pages. And they improved quite a little bit over the last years. Today, developers can use different types (number, tel, color, ...) and set different input modes (text, decimal, email, ...) to name two examples.

What remained tricky was to submit forms from within the scope of JavaScript. The HTMLFormElement defines a submit method, but it does not quite behave as one would expect.

HTML's default behavior and the not matching submit method

Section titled HTML's default behavior and the not matching `submit` method

Let's assume we have the following HTML form:

<form action="">
  <label>
    Your name
    <input type="text" required>
  </label>
  <button>Submit</button>
</form>

And some JavaScript:

document.querySelector('form')
  .addEventListener('submit', (event) => {
    // don't submit the form and
    // only log to the console
    event.preventDefault();
    console.log('submitted form');
  });

When one clicks the submit button the following happens:

  1. the form is validated and possible errors are shown
  2. if the form is valid, it fires a submit event
  3. the submit handler is called and it prevents the form submission due to event.preventDefault()

This triggered submit event gives developers a way to react to form submissions in JavaScript. And it's used a lot! Common scenarios in modern applications are to call preventDefault, make AJAX requests using JavaScript and replace the page contents dynamically.

But what happens when you get the form from the DOM and submit it in JavaScript via submit?

document.querySelector('form').submit();

The answer is – the form is submitted! (🤦‍♂️ duh!) What's surprising is that there won't be input validation, and there won't be a submit event. All the values are submitted no matter if the inputs are valid or not. This is unexpected behavior and it should behave like pressing the submit button. There are surely reason for skipping the validation, but I'd expect that submit also validates the form and only proceeds if everything is valid.

You can work around this problem by triggering the click on the submit button. click triggers the standard behavior that users see when they interact with a form, including validation and a fired submit event.

Mimicking, user behavior works fine and that's great – case closed! I never thought of it as elegant or pretty, though.

A new JavaScript method that validates forms before submitting

Section titled A new JavaScript method that validates forms before submitting

People started to work on a solution to this behavior in June 2019 (the proposal is an interesting read). The HTMLFormElement now includes an extra method called requestSubmit. And this method does the same as clicking a submit button. 🎉

There is no magic to it – it does what you expect and offers the great goodies HTML forms ship by default. I have to say – I'm excited about it!

submit requestSubmit
doesn't trigger submit event triggers submit event
doesn't trigger validation triggers validation
can't be canceled can be canceled via event.preventDefault in a submit event handler

The browser support as of November 2020 is as follows:

  • ✅ Chromium browsers (the new Microsoft Edge, Chrome, Opera, ...)
  • ✅ Firefox
  • ❌ Safari

Unfortunately, it's not cross browser supported yet.

You can read more about the requestSubmit method on MDN, read about it in the spec or see it in action on CodePen.

You can see a #devsheet visualizing the difference in the video below.

If you're interested in more reading more quick TIL ("today i learned") posts, subscribe to my monthly newsletter. 👋


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