calculate age from date field when age modifier specified on merge tag e.g. {Date of Birth:10:age}

rw-gf-age-calculation.php

<?php

class RW_GF_Age_Calculation {

    public function __construct() {
        add_action( 'init', array( $this, 'init' ) );
    }

    function init() {
        if ( ! class_exists( 'GFForms' ) || ! property_exists( 'GFForms', 'version' ) && version_compare( GFForms::$version, '1.9', '>=' ) ) {
            return;
        }

        add_filter( 'gform_pre_render', array( $this, 'maybe_output_script' ) );
        add_filter( 'gform_merge_tag_value_pre_calculation', array( $this, 'enable_age_modifier' ), 10, 6 );
    }

    function maybe_output_script( $form ) {
        $has_age_calculation = false;
        foreach ( $form['fields'] as $field ) {
            if ( ! $field->has_calculation() ) {
                continue;
            }

            if ( isset( $field->calculationFormula ) && strpos( $field->calculationFormula, ':age}' ) !== false ) {
                $has_age_calculation = true;
                break;
            }
        }

        if ( $has_age_calculation ) {
            $this->output_script();
        }

        return $form;
    }

    function output_script() {
        ?>
        <script type='text/javascript'>
            gform.addFilter('gform_merge_tag_value_pre_calculation', function (value, mergeTagArr, isVisible, formulaField, formId) {
                if (mergeTagArr[4] == 'age' && isVisible) {
                    var fieldId = parseInt(mergeTagArr[1]),
                        inputId = '#input_' + formId + '_' + fieldId,
                        datePicker = jQuery(inputId),
                        yearInput = jQuery(inputId + '_3'),
                        monthInput = jQuery(inputId + '_1'),
                        dayInput = jQuery(inputId + '_2'),
                        dateString = '';

                    if (datePicker.length == 1) {
                        dateString = datePicker.val();
                        var separator = '/',
                            reverse_date = false;

                        if (datePicker.hasClass('dmy')) {
                            reverse_date = true;
                        } else if (datePicker.hasClass('dmy_dash')) {
                            separator = '-';
                            reverse_date = true;
                        } else if (datePicker.hasClass('dmy_dot')) {
                            separator = '.';
                            reverse_date = true;
                        }

                        if (reverse_date) {
                            dateString = dateString.split(separator).reverse().join('/');
                        }
                    }

                    if (yearInput.length == 1 && monthInput.length == 1 && dayInput.length == 1) {
                        var dateField = [];
                        dateField[0] = yearInput.val();
                        dateField[1] = monthInput.val();
                        dateField[2] = dayInput.val();
                        if (dateField[0] != '' && dateField[1] != '' && dateField[2] != '') {
                            dateString = dateField.join('/');
                        }
                    }

                    if (dateString != '') {
                        // props: http://stackoverflow.com/questions/4060004/calculate-age-in-javascript/7091965#7091965
                        var today = new Date(),
                            birthDate = new Date(dateString),
                            m = today.getMonth() - birthDate.getMonth();

                        value = today.getFullYear() - birthDate.getFullYear();

                        if (m < 0 || ( m === 0 && today.getDate() < birthDate.getDate() )) {
                            value--;
                        }
                    }
                }
                return value;
            });
            gform.addAction('gform_post_calculation_events', function (mergeTagArr, formulaField, formId, calcObj) {
                var fieldId = parseInt(mergeTagArr[1]),
                    inputId = '#input_' + formId + '_' + fieldId,
                    dateField = jQuery(inputId + '_1, ' + inputId + '_2, ' + inputId + '_3');

                if (mergeTagArr[4] == 'age' && dateField.length == 3) {
                    console.log(dateField);
                    dateField.change(function () {
                        calcObj.bindCalcEvent(fieldId, formulaField, formId, 0);
                    });
                }
            });
        </script>
    <?php

    }

    function enable_age_modifier( $value, $input_id, $modifier, $field, $form, $entry ) {
        $target_field = RGFormsModel::get_field( $form, $input_id );

        if ( $target_field->type == 'date' && $modifier == 'age' ) {
            $dob   = rgar( $entry, $input_id );
            $today = new DateTime();
            $diff  = $today->diff( new DateTime( $dob ) );
            $value = $diff->y;
        }

        return $value;
    }

}

new RW_GF_Age_Calculation();

Hi, Thanks for this nice and awesome gist. Basically i'm looking for this code from long time, and i found it.
But can you plz write few line about how to use it? i have copied it to my function.php file, where to add the merge tag with :age?

can i use it to list field's column?

Thanks for this script. Would you be so kind to advice on how to implement it on Gravity Forms?

Great script, thanks for writing. I added the line :

if (dateField[0] < 1 || dateField[1] < 1 || dateField[2] < 1) {
    return 0;
}

to prevent the script calculating bogus ages when no value selected for one or two of day, month or year fields.