Form Validation in JavaScript Code

Form Validation in JavaScript Code
Code Snippet:JS Form Validation
Author: Abdullah Sajjad
Published: January 11, 2024
Last Updated: January 22, 2024
Downloads: 9,966
License: MIT
Edit Code online: View on CodePen
Read More

This JavaScript code snippet helps you to create a form validation feature on the form submit. It validates username, email, and password and displays the inline error message in case of invalid input. You can integrate this vanilla JavaScript code for registration/signup forms to validate inputs on submit.

This form validation snippet doesn’t require any additional library or plugin. It uses JavaScript regular expressions to validate emails. It allows setting min/max length rules for input validation.  Moreover, it can be integrated with your existing HTML forms.

How to Create Form Validation in JavaScript

1. First you need to create the HTML form element with username, email, and password input with validation attributes.

 <div class="container">
    <form id="form" class="form">
        <h2>Register With Us</h2>
        <div class="form-control">
            <label for="username">Username</label>
            <input type="text" id="username" placeholder="Enter Username">
            <small>Error Message</small>
        </div>
        <div class="form-control">
            <label for="email">Email</label>
            <input type="text" id="email" placeholder="Enter email">
            <small>Error Message</small>
        </div>
        <div class="form-control">
            <label for="password">Password</label>
            <input type="password" id="password" placeholder="Enter password">
            <small>Error Message</small>
        </div>
        <div class="form-control">
            <label for="password2">Confirm Password</label>
            <input type="password" id="password2" placeholder="Enter password again">
            <small>Error Message</small>
        </div>
        <button>Submit</button>
    </form>
</div>

2. After that, define the CSS styles for HTML form inputs, success, and error messages as follows.

:root{
    --succes-color: #2ecc71;;
    --error-color: #e74c3c;
}
.container{
    background-color: #fff;
    border-radius: 5px;
    box-shadow: 0 2px 10px rgba(0,0,0,0.3);
    width: 400px;
    margin: 10px auto;
}
h2{
    text-align: center;
    margin: 0 0 20px;
}
.form{
    padding: 30px 40px;
}
.form-control{
    margin-bottom: 10px;
    padding-bottom: 20px;
    position: relative;
}
.form-control label{
    color:#777;
    display: block;
    margin-bottom: 5px; 
}
.form-control input{
    border: 2px solid #f0f0f0;
    border-radius: 4px;
    display: block;
    width: 100%;
    padding: 10px;
    font-size: 14px;   
}
.form-control input:focus{
    outline: 0;
    border-color: #777;

}
.form-control.success input {
    border-color: var(--succes-color);
}
.form-control.error input {
    border-color: var(--error-color);    
}
.form-control small{
    color: var(--error-color);
    position: absolute;
    bottom: 0;
    left: 0;
    visibility: hidden;
}
.form-control.error small{
    visibility: visible;
}
.form button {
    cursor: pointer;
    background-color: #3498db;
    border: 2px solid #3498db;
    border-radius: 4px;
    color: #fff;
    display: block;
    padding: 10px;
    font-size: 16px;
    margin-top:20px;
    width:100%;
}

3. Finally, include the form validation JavaScript code in your project and done.

const form = document.getElementById('form');
const username = document.getElementById('username');
const email = document.getElementById('email');
const password = document.getElementById('password');
const password2 = document.getElementById('password2');

//Show input error messages
function showError(input, message) {
    const formControl = input.parentElement;
    formControl.className = 'form-control error';
    const small = formControl.querySelector('small');
    small.innerText = message;
}

//show success colour
function showSucces(input) {
    const formControl = input.parentElement;
    formControl.className = 'form-control success';
}

//check email is valid
function checkEmail(input) {
    const re = /^(([^<>()\[\]\\.,;:\s@"]+(\.[^<>()\[\]\\.,;:\s@"]+)*)|(".+"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$/;
    if(re.test(input.value.trim())) {
        showSucces(input)
    }else {
        showError(input,'Email is not invalid');
    }
}

//checkRequired fields
function checkRequired(inputArr) {
    inputArr.forEach(function(input){
        if(input.value.trim() === ''){
            showError(input,`${getFieldName(input)} is required`)
        }else {
            showSucces(input);
        }
    });
}

//check input Length
function checkLength(input, min ,max) {
    if(input.value.length < min) {
        showError(input, `${getFieldName(input)} must be at least ${min} characters`);
    }else if(input.value.length > max) {
        showError(input, `${getFieldName(input)} must be les than ${max} characters`);
    }else {
        showSucces(input);
    }
}

//get FieldName
function getFieldName(input) {
    return input.id.charAt(0).toUpperCase() + input.id.slice(1);
}

// check passwords match
function checkPasswordMatch(input1, input2) {
    if(input1.value !== input2.value) {
        showError(input2, 'Passwords do not match');
    }
}

//Event Listeners
form.addEventListener('submit',function(e) {
    e.preventDefault();

    checkRequired([username, email, password, password2]);
    checkLength(username,3,15);
    checkLength(password,6,25);
    checkEmail(email);
    checkPasswordMatch(password, password2);
}); 

That’s all! hopefully, this JavaScript validation plugin is helpful for you. If you have any questions or suggestions, let me know by comment below.

Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.

About CodeHim

Free Web Design Code & Scripts - CodeHim is one of the BEST developer websites that provide web designers and developers with a simple way to preview and download a variety of free code & scripts. All codes published on CodeHim are open source, distributed under OSD-compliant license which grants all the rights to use, study, change and share the software in modified and unmodified form. Before publishing, we test and review each code snippet to avoid errors, but we cannot warrant the full correctness of all content. All trademarks, trade names, logos, and icons are the property of their respective owners... find out more...