JSFiddle - React, Tailwind, and code Playground

HTML

<form name="inputFields">
      <input type="text" onChange="checkInput()" value="4" onKeyup="checkInput()"/>
      <input type="text" onChange="checkInput()" value="2" onKeyup="checkInput()"/>
      <input type="text" onChange="checkInput()" value="3" onKeyup="checkInput()"/>
      <input id="sendB" value="Submit" type="submit" disabled />
    </form>

JavaScript

(function(){
    var $inputs = document.forms['inputFields'].childNodes;
    for(var $i = 0; $i < $inputs.length; $i++) {
        if($inputs[$i].type == "text") {
            if(document.addEventListener) $inputs[$i].addEventListener('change', function(){
                document.getElementById('buttonID1').disabled = false;
            }, false);
            else $inputs[$i].attachEvent('onchange', function(){
                document.getElementById('buttonID1').disabled = false;
            });
        }
    }
})();