Intro to Form Validation with CSS Psuedo Selectors

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Intro to Form Validation with CSS Psuedo Selectors

Forms are a major part of most websites. While you may not need to create a form from scratch anymore, it’s good to know the fundamentals of forms. One aspect we’re going to look at is form validation.

A functional form should be able to validate users’ inputs from the client side. This can be done through CSS form validation.

Basic Form Functionality

The majority of basic forms are a simple contact form or login page. These forms require a few different areas of input. The goal is to make sure the user is forced to enter their information in correctly.

Data validation is making sure a user inputs correct information that is clean and can be used by the website. Syntax that has been input by the user must be valid, either a number or string for the website to read.

Form validation can be done in CSS through several pseudo selectors. Remember that pseudo selectors are like regular classes in HTML and CSS, but aren’t specifically stated in the markup. They will come up through a user’s action or external change of the document. A perfect example and use for them is in form validation. Here are your most important pseudo-selectors:

  • :valid – input elements selected that have valid values.
  • invalid – input elements that have invalid values.
  • :required -input elements will be selected that have the
  • specified “required” attribute.
  • disabled – input elements will be selected that have the specified “disabled” attribute.
  • :optional – input elements will be selected that have the specified not “required” attribute.

Validation Method Examples

Two of the previously listed pseudo-selectors allow the user to perfect form validation. These selectors are the valid and required selectors. One of the easiest and fastest ways to check for form validation is using the required pseudo selector. Letting your browser catch the error before anything is a fast and simple method.

<input required type="text" id=" firstName" name="firstName">

After that, you can write an alert message. This will pop off if they don’t fill out the required form. Another great feature is to use the :valid CSS pseudo selector. Your users need to know if they’ve entered in the correct data into the form. This can easily be done through adding a SVG to the side of the input forms.

The following syntax is how a :valid selector would be written:

& :valid {
        background: url(sample/image.svg);
        background-size: 10px;
        background-repeat: no-repeat;
        background-position: 10px 10px;

        */  Continue to hides the SVG logo (label) */
        & + label {
          opacity: 0;

Overall, these two selectors are the basis for proper client-side form validation. The majority of the time you will find a fully coded template for login.But, it is still helpful to know how to induce validation through the inputs required before passing data. A user interface element that guides the user and puts them on the correct path is important. Validation serves as an indispensable tool for interactivity with users.