JSFiddle - React, Tailwind, and code Playground

by chim

HTML

<input id="thisone" name="4e1c4b566ffff25798c18d49[username]" />
<div class="out">
test
</div>

JavaScript

$( function(){
var str="4e1c4b566ffff25798c18d49[username]"; 
var patt1=/\[.*\]/gi;    

    var inputName = $('#thisone').attr('name');
    
    $('.out').text( inputName.match(patt1) );
});