javascript - jQuery multiple selector with $(this) for Drop-down and Text-field -

$('#sb_height_questionnaire_afraid_of_heights ,     #tf_height_questionnaire_afraid_of_heights').on('change',function(){                         if ($(this[0]).val() == 'yes' || $(this[0]).val() == 'no'){         $("#hf_height_questionnaire_afraid_of_heights").val("are afraid of heights:"           + $(this[0]).val() + $(this[1]).val());       }  }); 

if yes or no selected something. onchange both select box , text-field example : https://jsfiddle.net/mkhizess/s9or1c20/

inside event hadndler, this refer changed element, not elements selected selector this[0] undefined.

so try

var $els = $('#sb_height_questionnaire_afraid_of_heights , #tf_height_questionnaire_afraid_of_heights').on('change', function () {     if ($(this).val() == 'yes' || $(this).val() == 'no') {         $("#hf_height_questionnaire_afraid_of_heights").val("are afraid of heights: " + $els.eq(0).val() + $els.eq(1).val());     } });