JSFiddle - React, Tailwind, and code Playground

HTML

<label>Valor 1:</label>
<input name="valor[]" type="number" />
<label>Valor 2:</label>
<input name="valor[]" type="number" />
<label>Valor 03:</label>
<input name="valor[]" type="number" />
<label>Valor 04:</label>
<input name="valor[]" type="number" />
<input type="button" onClick="somarValores()" value="botao">
<p id="resultado"></p>

JavaScript

var quant = document.getElementsByName("valor[]");
var teste = [];

function somarValores() {
    var soma = [].reduce.call(quant, function (somatorio, el) {
        return somatorio + parseInt(el.value, 10) || 0;
    }, 0);
    document.getElementById("resultado").innerHTML = soma;
}