JSFiddle - React, Tailwind, and code Playground

HTML

<form>
    <p>
        <label for="text">Blub</label>
        <input id="text" type="text" />
    </p>
    <p>
        <input id="submit" type="submit" />
    </p>
</form>

JavaScript

var submitBtn = document.getElementById("submit");
submitBtn.setAttribute('disabled', 'disabled');

if(document.getElementById("text")) {
    var textInput = document.getElementById("text");
    
    textInput.onkeyup = function() {
        if(this.value == '') {
            if(!submitBtn.hasAttribute('disabled')) {
                submitBtn.setAttribute('disabled', 'disabled');
            }
        } else {
            if(submitBtn.hasAttribute('disabled')) {
                submitBtn.removeAttribute('disabled');
            }
        }
    }
}