Populate Gravity Forms with dynamic population via JavaScript.

cssllc-gforms-js-prepopulation.php

<?php declare( strict_types=1 );
/**
 * Plugin name: CSSLLC Gravity Forms JavaScript Prepopulation
 * Plugin URI: https://gist.github.com/crstauf/5b6da3b818221ec0b408ae70a1cca232
 * Description: Populate Gravity Forms with dynamic population via JavaScript.
 * Author URI: https://develop.calebstauffer.com
 * Author: Caleb Stauffer
 * Version: 1.0
 */

class CSSLLC_GravityForms_JS_Prepopulation {

	/**
	 * @var string Input field attribute name.
	 */
	const ATTRIBUTE_NAME = 'data-gform-js-prepop';

	/**
	 * @var bool Check if there's at least one field with dynamic population.
	 */
	protected $has_prepop = false;

	/**
	 * Initialize.
	 *
	 * @return void
	 */
	public static function init() : void {
		static $once = false;

		if ( $once ) {
			return;
		}

		new self;

		$once = true;
	}

	/**
	 * Construct.
	 */
	protected function __construct() {
		add_filter( 'gform_field_content', array( $this, 'filter__gform_field_content' ), 10, 2 );
		add_action( 'gform_register_init_scripts', array( $this, 'action__gform_register_init_scripts' ) );
	}

	/**
	 * Filter: gform_field_content
	 *
	 * Add attribute to input field.
	 *
	 * @param string $markup
	 * @param object $field
	 *
	 * @return string
	 */
	public function filter__gform_field_content( $markup, $field ) : string {
		if ( ! $field->allowsPrepopulate || empty( $field->inputName ) ) {
			return $markup;
		}

		$this->has_prepop = true;

		$attribute = sprintf( '%s="%s"', self::ATTRIBUTE_NAME, esc_attr( $field->inputName ) );
		$markup    = str_replace( ' name=', ' ' . $attribute . ' name=', $markup );

		return $markup;
	}

	/**
	 * Action: gform_register_init_script
	 *
	 * Print JavaScript to populate the fields.
	 *
	 * @param array $form
	 *
	 * @return void
	 */
	public function action__gform_register_init_scripts( $form ) : void {
		static $once = false;

		if ( ! $this->has_prepop || $once ) {
			return;
		}

		ob_start();
		?>

		<script>
			( function() {

				const attribute_name = <?php echo json_encode( self::ATTRIBUTE_NAME ) ?>;
				const query_string   = window.location.search;
				const query_params   = new URLSearchParams( query_string );
				const prepop_fields  = document.querySelectorAll( 'input[' + attribute_name + ']' );

				if ( ! prepop_fields.length ) {
					return;
				}

				var field_id, field_prepop_parameter, query_param_value;

				prepop_fields.forEach( function( field ) {
					if ( ! field.hasAttribute( attribute_name ) ) {
						return;
					}

					field_prepop_parameter = field.getAttribute( attribute_name );

					if ( ! query_params.has( field_prepop_parameter ) ) {
						return;
					}

					query_param_value = query_params.get( field_prepop_parameter );

					if ( ! query_param_value.length ) {
						return;
					}

					document.querySelector( 'input#' + field.getAttribute( 'id' ) ).value = query_param_value;
				} );

			} () );
		</script>

		<?php
		$script = ob_get_clean();
		$script = str_replace( array( '<script>', '</script>' ), '', $script );

		$once = true;

		GFFormDisplay::add_init_script( $form['id'], __CLASS__, GFFormDisplay::ON_PAGE_RENDER, $script );
	}

}

CSSLLC_GravityForms_JS_Prepopulation::init();