JSFiddle - React, Tailwind, and code Playground

HTML

<input type="submit" name="sendNewSms" class="inputButton" id="sendNewSms" value=" Send " />

<input type="checkbox" id="disableBtn" />

JavaScript

var submit = document.getElementById('sendNewSms'),
    checkbox = document.getElementById('disableBtn'),
    disableSubmit = function(e) {
        submit.disabled = this.checked
    };

checkbox.addEventListener('change', disableSubmit);