JSFiddle - React, Tailwind, and code Playground

HTML

<input type="button" value="Run" id="b1"><br>
<table border=1 id="changeSubjectKatedra">
    <tr><td>someText<input type='hidden' value='someData'>
        </td><td>someText</td></tr>  
    <tr><td>someText2<input type='hidden' value='someData2'>
        </td><td>someText</td></tr>  
    <tr><td>someText3<input type='hidden' value='someData3'>
        </td><td>someText</td></tr>  
    <tr><td>someText<input type='hidden' value='someData'>
        </td><td>someText</td></tr>  
    <tr><td>someText<input type='hidden' value='someData'>
        </td><td>someText</td></tr>  
    <tr><td>someText4<input type='hidden' value='someData4'>
        </td><td>someText</td></tr>  



</table>

JavaScript

$("#b1").click(function() {
var rows = $("#changeSubjectKatedra tr");
for(var i = 0; i <= rows.length - 2; i++) {
    if ($(rows[i]).find("input").val() ==
        $(rows[i+1]).find("input").val()) {
         alert($(rows[i]).td.val());   
        }
}
    
});