Form Validation

The web

HTML has built-in support for validation of form elements. Among others, here are some of the attributes you can give form elements to have the browser validate them for you:
  • required - the element must be filled in
  • minlength - the element must be at least this many characters
  • maxlength - the element must be at most this many characters
  • min - the element must be at least this value
  • max - the element must be at most this value
  • pattern - the element must match this regular expression
For example, here's a form with a required text field and a required email field:
	<label for="name">Name</label>
	<input type="text" id="name" required />
	<label for="email">Email</label>
	<input type="email" id="email" required />
	<button type="submit">Submit</button>
The unfortunate truth here though is that you cannot rely on the browser to validate your forms for you. Users can easily bypass such validation by manually adding novalidate to the form tag or making the HTTP request directly using another tool. This is why it's important to validate your forms on the server. Client-side validation should be seen as a nice progressive enhancement for a better user experience, not a replacement for server-side validation.
As far as the server is concerned, there is no standard way to handle validation other than to respond with a 400 status code if there are validation errors. You typically want to respond with the error messages as well and then the client should display those error messages next to the form elements that failed validation.
There are important accessibility considerations when it comes to form validation, which we will address in the next exercise.

In Remix

Remix does not have any built-in support for form validation. However, it does have a nice way to get the error messages the server responds with using the useActionData() hook.