JSFiddle - React, Tailwind, and code Playground

HTML

<div class="panel-body">
    <div class="text-center">
        <button type="button" class="btn btn-info" onclick="loadTemp()">Temperatura</button>
    </div>
    <div class="panel-footer">
        <p class="text-center" id="temp">---</p>
    </div>
</div>

JavaScript

function loadTemp() {
    var xhttp = new XMLHttpRequest();
    xhttp.onreadystatechange = function() {
        if (xhttp.readyState == 4 && xhttp.status == 200) {
            temp.innerHTML = xhttp.responseText + ' ºC';
        }
    };
    xhttp.open("GET", "https://thingspeak.com/channels/116346/field/1/last.html", true);
    xhttp.send();
    return loadTemp;
}
var temp = document.getElementById("temp");
setInterval(loadTemp(), 5 * 60 * 1000);