JSFiddle - React, Tailwind, and code Playground

HTML

<div class=item>
    <label>Choose a reason</label>
    <select>
        <option value="iSuck">I rock!</option>
        <option value="iRock">I suck!</option>
        <option value="other">I have my own opinion</option>
    </select>
</div>
<div class="item">
    <label>Please explain</label>
    <input type="text" />
</div>
<div class="item">
    <input type="button" value="Submit" />
</div>

CSS

.item {display:inline-block;height:60px;vertical-align:top}
label {display:block;font-weight:bold}
.hidden {display:none}

JavaScript

// enable/disable hide a field based on a selected value
$("select")
    .on("change",function(e){
        var isFalse = $(this).val() !== "other";
        $("input").get(0).disabled = isFalse;
        $("input[type=text]").parents(".item").toggleClass("hidden",isFalse)
    }).change()