What You Need to Know About Client-Side Form Validation

Adam Stead
Published 02/28/2023
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Client Side ValidationGo onto any website or e-commerce store, and you’ll notice that almost everyone uses website forms. Whether it’s a checkout form, a booking form, a registration form, or a contact form, businesses are using web forms to streamline their user’s online experiences.

If you’re a customer-centric company that wants to create forms for your website, you need to know about client-side form validation. It’s how you can provide users with an efficient, helpful form-filling experience while ensuring that all the data your users submit is secure, consistent, and valid.

Client-side validation forms are focused on user experience, which is probably why it’s such an important part of creating checkout, registration, and lead generation forms. In fact, web forms are the most highly-utilized and effective lead capture tool according to HubSpot – they’re used by 74% of marketers and boast high conversion rates.

To truly understand what client-side form validation is, it helps to understand what form validation is first.

What is Form Validation?

Chart of types of lead capture form tools

Let’s say you want to sign up to receive a deal from your favorite online store. To complete the signup process, you’ll have to type your information (name, phone number, address, etc.) into a registration form.

If you don’t enter your data correctly, the form will send you what’s called a validation message. Validation messages are often displayed in red above or below the form field.

Common validation messages include:

  • “This field is required”: This means that you’ve left the field blank).
  • “Please enter in format DD/MM/YYY”: You’ve entered data in the wrong format.
  • “Your password should be between 8 and 30 characters long and contain one uppercase letter, one number, and one symbol”: There are strict data format requirements for this field.



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So, for example, if a user entered their email address in the wrong format, a validation message might pop up that looks like this:

Form validation messages are configured by developers to alert the user that there’s something wrong with the data they’ve inputted. Good form validation messages let the user know what they can do to fix the problem (e.g, instead of simply saying “invalid input”, a good validation message might say “please input phone number in xxx-xxxx format.”

Why Form Validation is Important

Form validation is important for four key reasons:

  1. It’s critical to website security: There are lots of ways that malicious users can abuse forms. Unprotected forms are vulnerable to SQL injection attacks, cross-site scripting, and much more. Form validation enhances web security and consumer safety by applying strict constraints on valid inputs.
  2. It prevents human error: Form validation mitigates the risk of users inputting the wrong data (such as the wrong zip code or phone number). Wrongly-inputted data can result in order delays, poor customer service, etc., which is why form validation is crucial for delivering positive customer experiences.
  3. It protects your users’ data: Form validation for passwords verifies that users are only inputting highly-secure passwords. This protects their account information from data breaches and malicious attacks.
  4. It enforces data consistency: Freeform data can cause chaos in your database and, at worse, even crash your applications. Form validation is a critical step in creating a foundation for database consistency. And, because you can integrate your forms with your other tools for e-commerce (such as your CRMs and email marketing platforms), you can extend your data consistency even further.

So, now you know what form validation is, let’s explore it more deeply. There are two types of form validation: server-side validation and client-side validation. While this article will focus on client-side form validation, it helps to have a basic understanding of what server-side form validation is, too.

What is Server-Side Form Validation?

As opposed to client-side validation (which is completed in the browser), server-side validation takes place on the server.

Once a user submits data into a form, the browser sends this data to the server. The server will then validate the data against the constraints and requirements set by the application.

If the data is valid, it will be saved to the database. If it’s invalid, it will be sent back to the browser along with an error message explaining what went wrong.

The problem with server-side validation is that it takes time to process. Also, it can only be completed after the user completes the whole form. This means that users must wait until they’ve submitted the entire form to be notified of any errors.

If your user has a poor network connection, this can make for a frustrating, tedious experience.

So, while server-side form validation is absolutely necessary for protecting your online store from cyber attacks, it doesn’t exactly provide a good experience for your users.

The answer? Client-side form validation.

So, What is Client-Side Form Validation?

Client-side form validation occurs on your site’s front end before the browser submits the data to the server. Instead, the browser itself will complete the validation process first, checking the inputted data and providing the user with an immediate response.

You can think of client-side form validation as your first line of defense. It protects the integrity of your back end from badly formatted data. And, by providing users with immediate, easy-to-understand custom error messages, you can deliver a better user experience.

There are two different ways that you can implement client-side form validation: built-in form validation and JavaScript validation.

JavaScript Validation

JavaScript validation is coded using JavaScript and is more customizable than built-in form validation. It gives you more control over the design, feel, and microcopy of your validation messages, allowing you to create forms that express your brand’s identity.

However, as you can probably guess, validating forms using JavaScript requires pretty extensive coding knowledge and stricter continuous testing processes in response to code changes.

For this reason, many developers are turning to built-in form validation instead. Built-in form validation creates better internal workflows and provides simpler, to-the-point forms. In turn, businesses can provide more optimal user experiences.

Built-in Form Validation

Built-in form validation uses HTML5 to perform data validation instead of the more traditionally-used JavaScript. It’s well-supported by popular modern browsers (Safari, Firefox, etc.) which makes it a fantastic modern form control for those who aren’t a fan of writing JavaScript code.

Its ability to independently validate user data is made possible through the use of validation attributes of the form elements. For example:

  • “Type”: Defines the specific type of data that should be inputted (email address, URL, phone number, etc,).
  • “Required”: Marks the form field as mandatory, meaning it must be filled in before submission.
  • “Minlength” and “maxlength”: Specifies and enforces control over the minimum and maximum character length.
  • “Pattern”: Dictates regular expression (pattern) rules that the inputted data needs to abide by for validation.

Built-in form validation offers users visual aids to guide them to successful form completion. They are presented using CSS pseudo-classes, which let you define special states of elements.

For example:

  • :invalid and :valid tell users which elements abide by validation rules and which ones require revision.
  • :required and :optional inform the user of the mandatory state of the field.
  • :inrange and :out-of-range inform users that their inputted data value is either within or outside the allowed limit.

Built-in form validation is useful, but it doesn’t provide the same customizability as JavaScript validation.

Best Practices for Your Client-Side Form Validation Messages

Improve the effectiveness of your forms by getting them right the first time. Here are a few simple best practices to follow as you create your web forms.

  • Design your forms with web accessibility and inclusivity in mind. Are your forms easy to read and interpret? Are they optimized for mobile devices and screen readers?
  • Make them clear and concise. Your website forms should be clutter-free and intuitive to navigate.
  • Utilize integrations. Did you know that you can integrate your forms with third-party e-commerce tools, such as your CRM? This gives forms the ability to automatically send inputted information to your other disparate tools, improving internal workflows and data consistency. Before making your form live, test the performance of your integrations to verify that the form is sending data correctly.
  • If you validate forms with JavaScript, invest in your exploratory testing process. Enlist the help of diverse global testers (testers using different browsers, languages, etc.) and let them functionally investigate your forms to test their performance on the client side.

Screenshot from computer.org

Final Takeaways

Client-side form validation is essentially a user-experience-focused initiative. While server-side form validation protects your back-end from bad data corruption and is the hardened defense against malicious attacks, form validation on the client side aims to attend to the needs of your end users.

By providing your users with instant, easy-to-follow error messages, you make the sometimes-tedious process of filling out forms a much smoother experience.

Client-end form validation can even act as a deterrent for opportunist hackers, who are more likely to flee if they realize you’re well-protected.

Popular free website builders like WordPress have a range of plugins that offer customizable form templates and built-in validations. In the case of popular plugins like WPForms, you can simply customize your forms using CSS.

About the Writer

Adam Stead is a Content Marketer at Global App Testing, a best-in-class software testing company that has helped top apps, including Google, Microsoft, Facebook, and Craigslist deliver high-quality software in markets across the world with various processes like mobile app deployment with Global App Testing. Adam has 10 years of experience in editing, content creation, and digital marketing within the tech section, with a wealth of Social Media Marketing, Content Creation, Project Management, Podcasting, and Graphic Design skills. You can find him on LinkedIn.