JSFiddle - React, Tailwind, and code Playground

HTML

<form method="get" action="" name="suma">
    <select name="eventType">
        <option value="submit">submit</option>
        <option value="input" >input</option>
    </select>
    <input type="text" name="num1" />
    +
    <input type="text" name="num2" />
    =
    <output name="result"></output>
    <input type="submit" value="resultado"/>
</form>

CSS

select, input[type="submit"] {
    display: block;
}

JavaScript

window.addEventListener( "load", function(){

    var formSuma  = document.forms.suma;
    var eventType = formSuma.eventType.value;
    formSuma.eventType.addEventListener( "change", function(){
        console.log( formSuma.eventType.value );
    });

    formSuma.addEventListener( formSuma.eventType.value, function(){
        console.log( "eo" );
    });
});