JSFiddle - React, Tailwind, and code Playground

HTML

<div style="display:inline; border: 1px solid black; height:30px;">
    <span>This is my text that I want to fit ssssssssssssssssssssssssssssssss s</span>
</div>

JavaScript

$(function() {
    var span = $('span');
    var fontSize = parseInt(span.css('font-size'));

    do {
        fontSize--;
        span.css('font-size', fontSize.toString() + 'px');
    } while (span.height() >= 20);
});