JSFiddle - React, Tailwind, and code Playground

HTML

<div id='box1'>
    <div id='box2'>
    </div>
</div>
<p id="w"></p>
<p id="iw"></p>

CSS

#box1 {
    width:100px;
    height:100px;
    overflow:auto;
}

#box2 {
    width:200px;
    height:200px;
    background-color:#aaa;
    
}

JavaScript

$('#box1').html("<img src='http://lorempixel.com/output/people-h-c-1449-1723-4.jpg' />");

var helperDiv = $('<div />');
$('#box1').append(helperDiv);

$('#iw').text("inner width is: " + helperDiv.width());
helperDiv.remove();