Best tweaks for Gravity Forms plugin for creating forms with WordPress. Enhance Bootstrap 4 compatibility and increase performances. More informations in this tutorial: https://wpchannel.com/wordpress/tutoriels-wordpress/astuces-optimiser-formulaires-gravity-forms

mu-gravity-forms.php

<?php if (!defined('ABSPATH')) die('Restricted Area');


/*
* Plugin Name: Gravity Forms Enhancements
* Description: Tweaks for Gravity Forms plugin.
* Version: 20191102
* Author: Aurélien Denis
* Author URI: https://wpchannel.com/
*/


/* Check if Gravity Forms is available */
include_once(ABSPATH . 'wp-admin/includes/plugin.php');
if (is_plugin_active('gravityforms/gravityforms.php')) {

	/* JS in Footer */
	add_filter('gform_init_scripts_footer', '__return_true');
	
	function wpc_gform_cdata_open($content = '') {
		$content = 'document.addEventListener("DOMContentLoaded", function() { ';
		return $content;
	}
	add_filter('gform_cdata_open', 'wpc_gform_cdata_open');
	
	function wpc_gform_cdata_close($content = '') {
		$content = ' }, false);';
		return $content;
	}
	add_filter('gform_cdata_close', 'wpc_gform_cdata_close');


	/* Change Submit Button */
	function wpc_gf_input_to_button($button, $form) {
		$dom = new DOMDocument();
		$dom->loadHTML($button);
		$input = $dom->getElementsByTagName('input')->item(0);
		$new_button = $dom->createElement('button');
		$new_button->appendChild($dom->createTextNode($input->getAttribute('value')));
		$input->removeAttribute('value');
		foreach($input->attributes as $attribute) {
			$new_button->setAttribute($attribute->name, $attribute->value);
		}
		$input->parentNode->replaceChild($new_button, $input);
		return $dom->saveHtml($new_button);
	}
	add_filter('gform_next_button', 'wpc_gf_input_to_button', 10, 2);
	add_filter('gform_previous_button', 'wpc_gf_input_to_button', 10, 2);
	add_filter('gform_submit_button', 'wpc_gf_input_to_button', 10, 2);


	/* Add Bootstrap 4 Classes on Submit Button */
	function wpc_gf_custom_css_classes($button, $form) {
		$dom = new DOMDocument();
		$dom->loadHTML($button);
		$input = $dom->getElementsByTagName('button')->item(0);
		$classes = $input->getAttribute('class');
		$classes .= " btn btn-primary text-uppercase";
		$input->setAttribute('class', $classes);
		return $dom->saveHtml($input);
	}
	add_filter('gform_submit_button', 'wpc_gf_custom_css_classes', 10, 2);
	
	
	/* Add Bootstrap 4 Classes on Fields */
	function wpc_gf_bs4($content, $field, $value, $lead_id, $form_id) {
		if ($field["type"] != 'hidden' && $field["type"] != 'list' && $field["type"] != 'checkbox' && $field["type"] != 'html' && $field["type"] != 'address') {
			$content = str_replace('class=\'medium', 'class=\'form-control medium', $content);
			$content = str_replace('class=\'large', 'class=\'form-control large', $content);
		}
		if ($field["type"] == 'name' || $field["type"] == 'address') {
			$content = str_replace('<input ', '<input class=\'form-control\' ', $content);
		}
		if ($field["type"] == 'textarea') {
			$content = str_replace('class=\'textarea', 'class=\'form-control textarea', $content);
		}
		if ($field["type"] == 'consent') {
			$content = str_replace('<input ', '<input class=\'custom-control-input\' ', $content);
			$content = str_replace('gfield_consent_label', 'gfield_consent_label custom-control-label', $content);
		}
		return $content;
	}
	add_filter('gform_field_content', 'wpc_gf_bs4', 10, 5);
	

	/* Add Bootstrap 4 Validation Message */
	function wpc_gf_validation($message, $form) {
		return "<div class='validation_error alert alert-danger'>" . esc_html__('There was a problem with your submission.', 'gravityforms') . ' ' . esc_html__('Errors have been highlighted below.', 'gravityforms') . '</div>';
	}
	add_filter('gform_validation_message', 'wpc_gf_validation', 10, 2);
}