JavaScript Prevent Form Submit Until Validation

JavaScript Prevent Form Submit Until Validation
Code Snippet:Form Validation: Validate on Submit
Author: Chris Ferdinandi
Published: January 12, 2024
Last Updated: January 22, 2024
Downloads: 525
License: MIT
Edit Code online: View on CodePen
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This JavaScript code helps you to create a functionality to prevent form submit until validation is complete. It adds the "novalidate" attribute to the form, ensuring that HTML5 native validation is bypassed. The code then validates each form field on blur, displaying relevant error messages and styling.

On form submission, it checks all fields for errors, preventing submission if any are found and focusing on the first erroneous field. This ensures user-entered data meets specified criteria for name, email, URL, and radio buttons.

You can integrate this code to enhance your form’s user experience and data accuracy.

How to Create Functionality in JavaScript to Prevent Form Submit Until Validation

1. First, copy and paste the following HTML code into your web page. This code includes a simple form with fields for name, email, URL, and radio buttons. Ensure your form has the class "validate" for the JavaScript code to target.

<form class="validate" action="#">
	<div>
		<label for="text">Name</label>
		<input type="text" id="text" required>
	</div>

	<div>
		<label for="email">Email</label>
		<input type="email" id="email" title="The domain portion of the email address is invalid (the portion after the @)." pattern="^([^\x00-\x20\x22\x28\x29\x2c\x2e\x3a-\x3c\x3e\x40\x5b-\x5d\x7f-\xff]+|\x22([^\x0d\x22\x5c\x80-\xff]|\x5c[\x00-\x7f])*\x22)(\x2e([^\x00-\x20\x22\x28\x29\x2c\x2e\x3a-\x3c\x3e\x40\x5b-\x5d\x7f-\xff]+|\x22([^\x0d\x22\x5c\x80-\xff]|\x5c[\x00-\x7f])*\x22))*\x40([^\x00-\x20\x22\x28\x29\x2c\x2e\x3a-\x3c\x3e\x40\x5b-\x5d\x7f-\xff]+|\x5b([^\x0d\x5b-\x5d\x80-\xff]|\x5c[\x00-\x7f])*\x5d)(\x2e([^\x00-\x20\x22\x28\x29\x2c\x2e\x3a-\x3c\x3e\x40\x5b-\x5d\x7f-\xff]+|\x5b([^\x0d\x5b-\x5d\x80-\xff]|\x5c[\x00-\x7f])*\x5d))*(\.\w{2,})+$" required>
	</div>

	<div>
		<label for="url">URL</label>
		<input type="url" id="url" title="The URL is a missing a TLD (for example, .com)." pattern="^(?:(?:https?|HTTPS?|ftp|FTP):\/\/)(?:\S+(?::\S*)?@)?(?:(?!(?:10|127)(?:\.\d{1,3}){3})(?!(?:169\.254|192\.168)(?:\.\d{1,3}){2})(?!172\.(?:1[6-9]|2\d|3[0-1])(?:\.\d{1,3}){2})(?:[1-9]\d?|1\d\d|2[01]\d|22[0-3])(?:\.(?:1?\d{1,2}|2[0-4]\d|25[0-5])){2}(?:\.(?:[1-9]\d?|1\d\d|2[0-4]\d|25[0-4]))|(?:(?:[a-zA-Z\u00a1-\uffff0-9]-*)*[a-zA-Z\u00a1-\uffff0-9]+)(?:\.(?:[a-zA-Z\u00a1-\uffff0-9]-*)*[a-zA-Z\u00a1-\uffff0-9]+)*(?:\.(?:[a-zA-Z\u00a1-\uffff]{2,}))\.?)(?::\d{2,5})?(?:[/?#]\S*)?$" required>
	</div>

	<div>
		<strong>Radio Buttons</strong>
		<label class="label-normal">
		    <input type="radio" name="radio" id="radio-1" required>
		    Yes
		</label>
		<label class="label-normal">
		    <input type="radio" name="radio" id="radio-2" required>
		    No
		</label>
	</div>

	<input type="submit" class="button" value="Submit">
</form>

2. Copy the following CSS code into your stylesheet. These styles ensure a visually appealing and user-friendly form. You can customize the styles according to your website’s design.

body {
	font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "Roboto", "Oxygen", "Ubuntu", "Cantarell", "Fira Sans", "Droid Sans", "Helvetica Neue", sans-serif;
	font-size: 112.5%;
}  

/**
 * Form Styles
 */

form{
   background: #fff;
   padding: 12px;
}
label {
	display: block;
	font-weight: bold;
	margin-bottom: 0.5em;
}

.label-normal {
	font-weight: normal;
}

.description-date {
	color: #808080;
	font-size: 0.8em;
	font-weight: normal;
}

.supports-date .description-date {
    display: none;
}

input,
select {
	display: inline-block;
	font-size: 1em;
	margin-bottom: 1em;
	padding: 0.25em 0.5em;
	width: 100%;
     box-sizing: border-box;
}

[type="checkbox"],
[type="radio"] {
	margin-bottom: 0.5em;
	width: auto;
}

.button {
	background-color: #0088cc;
	border: 1px solid #0088cc;
	border-radius: 1px;
	color: #ffffff;
	display: inline-block;
	font-size: 0.9375em;
	font-weight: normal;
	line-height: 1.2;
	margin-right: 0.3125em;
	margin-bottom: 0.3125em;
	padding: 0.5em 0.6875em;
	width: auto;
}

.button:active,
.button:focus,
.button:hover {
	background-color: #005580;
	border-color: #005580;
	color: #ffffff;
	text-decoration: none;
}

.button:active {
	box-shadow: inset 0 0.15625em 0.25em rgba(0, 0, 0, 0.15), 0 1px 0.15625em rgba(0, 0, 0, 0.05);
}

/**
 * Errors
 */
.error {
	border-color: red;
}

.error-message {
	color: red;
	font-style: italic;
	margin-bottom: 1em;
}

3. Finally, copy and paste the JavaScript code at the end of your HTML file or include it in a separate script file. This code adds the “novalidate” attribute to your form, disabling native HTML5 validation. It then implements custom validation logic for each field, showing error messages on blur and preventing form submission if errors exist.

// Add the novalidate attribute when the JS loads
var forms = document.querySelectorAll('.validate');
for (var i = 0; i < forms.length; i++) {
    forms[i].setAttribute('novalidate', true);
}


// Validate the field
var hasError = function (field) {

    // Don't validate submits, buttons, file and reset inputs, and disabled fields
    if (field.disabled || field.type === 'file' || field.type === 'reset' || field.type === 'submit' || field.type === 'button') return;

    // Get validity
    var validity = field.validity;

    // If valid, return null
    if (validity.valid) return;

    // If field is required and empty
    if (validity.valueMissing) return 'Please fill out this field.';

    // If not the right type
    if (validity.typeMismatch) {

        // Email
        if (field.type === 'email') return 'Please enter an email address.';

        // URL
        if (field.type === 'url') return 'Please enter a URL.';

    }

    // If too short
    if (validity.tooShort) return 'Please lengthen this text to ' + field.getAttribute('minLength') + ' characters or more. You are currently using ' + field.value.length + ' characters.';

    // If too long
    if (validity.tooLong) return 'Please shorten this text to no more than ' + field.getAttribute('maxLength') + ' characters. You are currently using ' + field.value.length + ' characters.';

    // If number input isn't a number
    if (validity.badInput) return 'Please enter a number.';

    // If a number value doesn't match the step interval
    if (validity.stepMismatch) return 'Please select a valid value.';

    // If a number field is over the max
    if (validity.rangeOverflow) return 'Please select a value that is no more than ' + field.getAttribute('max') + '.';

    // If a number field is below the min
    if (validity.rangeUnderflow) return 'Please select a value that is no less than ' + field.getAttribute('min') + '.';
  
      // If pattern doesn't match
    if (validity.patternMismatch) {

        // If pattern info is included, return custom error
        if (field.hasAttribute('title')) return field.getAttribute('title');

        // Otherwise, generic error
        return 'Please match the requested format.';

    }

    // If all else fails, return a generic catchall error
    return 'The value you entered for this field is invalid.';

};


// Show an error message
var showError = function (field, error) {

    // Add error class to field
    field.classList.add('error');
  
    // If the field is a radio button and part of a group, error all and get the last item in the group
    if (field.type === 'radio' && field.name) {
        var group = document.getElementsByName(field.name);
        if (group.length > 0) {
            for (var i = 0; i < group.length; i++) {
                // Only check fields in current form
                if (group[i].form !== field.form) continue;
                group[i].classList.add('error');
            }
            field = group[group.length - 1];
        }
    }

    // Get field id or name
    var id = field.id || field.name;
    if (!id) return;

    // Check if error message field already exists
    // If not, create one
    var message = field.form.querySelector('.error-message#error-for-' + id );
    if (!message) {
        message = document.createElement('div');
        message.className = 'error-message';
        message.id = 'error-for-' + id;
        
        // If the field is a radio button or checkbox, insert error after the label
        var label;
        if (field.type === 'radio' || field.type ==='checkbox') {
            label = field.form.querySelector('label[for="' + id + '"]') || field.parentNode;
            if (label) {
                label.parentNode.insertBefore( message, label.nextSibling );
            }
        }

        // Otherwise, insert it after the field
        if (!label) {
            field.parentNode.insertBefore( message, field.nextSibling );
        }

    }
    
    // Add ARIA role to the field
    field.setAttribute('aria-describedby', 'error-for-' + id);

    // Update error message
    message.innerHTML = error;

    // Show error message
    message.style.display = 'block';
    message.style.visibility = 'visible';

};


// Remove the error message
var removeError = function (field) {

    // Remove error class to field
    field.classList.remove('error');
    
    // Remove ARIA role from the field
    field.removeAttribute('aria-describedby');

    // If the field is a radio button and part of a group, remove error from all and get the last item in the group
    if (field.type === 'radio' && field.name) {
        var group = document.getElementsByName(field.name);
        if (group.length > 0) {
            for (var i = 0; i < group.length; i++) {
                // Only check fields in current form
                if (group[i].form !== field.form) continue;
                group[i].classList.remove('error');
            }
            field = group[group.length - 1];
        }
    }

    // Get field id or name
    var id = field.id || field.name;
    if (!id) return;
    

    // Check if an error message is in the DOM
    var message = field.form.querySelector('.error-message#error-for-' + id + '');
    if (!message) return;

    // If so, hide it
    message.innerHTML = '';
    message.style.display = 'none';
    message.style.visibility = 'hidden';

};


// Listen to all blur events
document.addEventListener('blur', function (event) {

    // Only run if the field is in a form to be validated
    if (!event.target.form.classList.contains('validate')) return;

    // Validate the field
    var error = hasError(event.target);
  
    // If there's an error, show it
    if (error) {
        showError(event.target, error);
        return;
    }

    // Otherwise, remove any existing error message
    removeError(event.target);

}, true);


// Check all fields on submit
document.addEventListener('submit', function (event) {

    // Only run on forms flagged for validation
    if (!event.target.classList.contains('validate')) return;

    // Get all of the form elements
    var fields = event.target.elements;

    // Validate each field
    // Store the first field with an error to a variable so we can bring it into focus later
    var error, hasErrors;
    for (var i = 0; i < fields.length; i++) {
        error = hasError(fields[i]);
        if (error) {
            showError(fields[i], error);
            if (!hasErrors) {
                hasErrors = fields[i];
            }
        }
    }

    // If there are errrors, don't submit form and focus on first element with error
    if (hasErrors) {
        event.preventDefault();
        hasErrors.focus();
    }

    // Otherwise, let the form submit normally
    // You could also bolt in an Ajax form submit process here

}, false);

If needed, customize the validation rules in the JavaScript code to match your specific requirements. You can adjust the error messages, validation patterns, and field-specific criteria based on your application’s needs.

That’s all! hopefully, you have successfully created a functionality in JavaScript to prevent form submit until validation process. If you have any questions or suggestions, feel free to comment below.

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