JSFiddle - React, Tailwind, and code Playground

HTML

<div id="testdiv"></div>

<input type="textbox" id="txtbox" value="some string"/>

CSS

#testdiv
{
    position: absolute;
    visibility: hidden;
    height: auto;
    width: auto;
}

JavaScript

$(document).ready(function() {
    $("#txtbox").keyup(function() {
        var the_Text = $("#txtbox").val();
        
        var width = $("#testdiv").text(the_Text).width();
        
        alert("The text width is : " + width + " px");
    });
});