Answer by FoxInFlame for Only require textfield when radio is selected. ZF2

You can use the JavaScript library jQuery to do this.

$(document).ready(function() {   $("#Radiobuttons").click(function() {       if($(this).attr('id') == "Other") {            //IF THE ID IS "OTHER"            $("#foo").show();                  }  else {            //IF THE ID IS NOT "OTHER"            $("#foo").hide();          }   });});

Because with just this, the user can submit the form with the text box empty, and the check box ticked, you can use this script.

//CHECK IF THE FORM IS SUBMITTEDif ( $("#foo").css('display') != 'none' ){    //The text box is visible. Now check if it's empty, with    //jQuery, PHP, or any other thing you use.}