Limit the number of "favorites" in radio buttons

In the latest version of the MB Frontend Submission plugin, I added some code to disable the submit button when it's already clicked (to prevent duplicated submission). You can take it as a sample and write your own code, like this:

function count_favorites() {...}

$( 'input[type="radio"]' ).on( 'change', function() {
    var $submitButton = $( '.rwmb-form-submit' ).children( 'button' );
    if ( count_favorites() > 3 ) {
        $submitButton.prop( 'disabled', true );
    } else {
        $submitButton.prop( 'disabled', false );
    }
} );

Please try this:

jQuery(document).ready(function( $ ){
  $('.count input').attr('readonly', true);
  $('.radio').change(function () {
    // Counting.
    var count=0;
    $('.radio input:checked').each(function(){
      if ($(this).val().replace(/V_/g,'')=="Specialiteit") {
        count += 1;
      }
    });
    $('.count input').val(count);

    var $submitButton = $( '.rwmb-form-submit' ).children( 'button' );
    if ( count > 3 ) {
      $submitButton.prop( 'disabled', true );
    } else {
      $submitButton.prop( 'disabled', false );
    }
  });
});

Ah, I forgot to tell you that the code above only add or remove disabled attribute for the button. The disabled makes the button un-clickable. However, it doesn't change the style. You might need to add something like this to the theme's CSS:

button[disabled] { background: #999 }