JSFiddle - React, Tailwind, and code Playground

HTML

<select id="dropBox" size="1" onChange="dropBoxChng();">
    <option value="1">Choice 1</option>
    <option value="2">Choice 2</option>
    <option value="3">Choice 3</option>
    <option value="4">Other</option>
</select>


<input type="text" id="txtBox" style="display:none">

<script type='text/javascript'>
    function dropBoxChng(){
    if(document.getElementById('dropBox').value == 2){
    document.getElementById('txtBox').style.display = 'block';
    }
    }
</script>