JSFiddle - React, Tailwind, and code Playground

HTML

<input type="text" id="searchuser" value="Zoek" />
<input type="button" id="gosearchuser" value=">" />


<div id="onlineList">
       <div  id="ajaxChat_u_109" name="username1" data-gender="8">whatever1</div>
       <div  id="ajaxChat_u_109" name="username2" data-gender="8">whatever2</div>
       <div  id="ajaxChat_u_109" name="username3" data-gender="8">whatever3</div>
       <div  id="ajaxChat_u_109" name="username4" data-gender="8">whatever4</div>
       <div  id="ajaxChat_u_109" name="username5" data-gender="8">whatever5</div>
       <div  id="ajaxChat_u_109" name="username6" data-gender="8">whatever6</div>
       <div  id="ajaxChat_u_109" name="username7" data-gender="8">whatever7</div>
    </div>

JavaScript

$("#gosearchuser").on("click", function (event) {
    var $searchparam = $('#searchuser').val();
        $('div[name*="' + $searchparam + '"]').hide();
});