How to add a custom attribute?

Question

How to add a custom attribute in the field Contact Form 7 without javascript ?

For example, there is such a field on the page:

Answer 1

Find the name of your field.

[text* text-21]

If the name of your field name="text-21", like in my example, add this code to functions.php file.

add_filter( 'wpcf7_form_elements', 'imp_wpcf7_form_elements' );
function imp_wpcf7_form_elements( $content ) {
    $str_pos = strpos( $content, 'name="text-21"' );
    if ( $str_pos !== false ) {
        $content = substr_replace( $content, ' data-attr="custom" data-msg="Foo Bar 1" ', $str_pos, 0 );
    }
    return $content;
}

Note, it will add those attributes to all forms elements where the name is text-21, if you want prevent it then give your form element some unique name [text* unique-name]

And change the code to

add_filter( 'wpcf7_form_elements', 'imp_wpcf7_form_elements' );
function imp_wpcf7_form_elements( $content ) {
    $str_pos = strpos( $content, 'name="unique-name"' );
    if ( $str_pos !== false ) {
        $content = substr_replace( $content, ' data-attr="custom" data-msg="Foo Bar 1" ', $str_pos, 0 );
    }
    return $content;
}