JSFiddle - React, Tailwind, and code Playground

HTML

<textarea name="ctl00$m$g_c6ae303a_6013_4adb_8057_63a214bcfd24$ctl00$ctl04$ctl08$ctl00$ctl00$ctl04$ctl00$ctl00$UserField$downlevelTextBox" rows="1" cols="20" id="ctl00_m_g_c6ae303a_6013_4adb_8057_63a214bcfd24_ctl00_ctl04_ctl08_ctl00_ctl00_ctl04_ctl00_ctl00_UserField_downlevelTextBox" class="ms-input" Title="People Picker" AutoPostBack="0" >
</textarea>

JavaScript

$('textarea.ms-input').change(function(){
    if($.trim(this.value) == ''){
        alert("Look maw, no content!");   
    }
});