soft-limit-community-events-title-length.php

<?php
/**
 * Adds some JS to enforce a limit on the length of the submitted title.
 * 
 * Modify the limit value (`var limit = 65`) according to your needs, etc.
 * Remember that this is frontend only, nothing is enforced server side.
 * 
 * Tested with Community Events 4.5.9.
 */
add_action( 'tribe_events_community_form', function() {
    echo '
        <script defer>
            jQuery( document ).ready( function( $ ) { 
                var limit = 65;
                var $warning_label;
                var $post_title = $( "#post_title" );

                function create_warning_label() {
                    $warning_label = $( "<p><b>The title must be " + limit + " characters or less!</b></p>" );
                    $warning_label.hide();
                    $( ".events-community-post-title" ).append( $warning_label );
                }

                function on_change() {
                    var title = $post_title.val();

                    // Display warning and truncate title if necessary
                    if ( title.length > limit ) {
                        $warning_label.show();
                        $post_title.val( title.substr( 0, limit ) );
                    }
                    else {
                        $warning_label.hide();
                    }
                }

                create_warning_label();
                $post_title.on( "input", on_change );
            } );
        </script>
    ';
}, 20 );