ildarmustafin,
скопируйте этот код и создайте новую страницу у себя для теста.
<!doctype html>
<html lang="ru">
<head>
<meta http-equiv="Content-type" content="text/html; charset=utf-8">
<title>TEST</title>
<meta name="viewport" content="width=device-width, initial-scale=1.0">
</head>
<body>
<span class="input-group-text">input1:</span>
<input type="number" id="in1" value="110">
<span class="input-group-text">input2:</span>
<input type="number" id="in2" value="84">
<input id="getzp" type="submit" value="Расчет ЗП" onclick="getZp();">
<div class="w-100" id="t1">SUMMA:</div>
<div id="t2">SECOND:</div>
<script>
var sec_left = 0;
window.onload = function() {
window.setInterval(function () { getCountSec();}, 1000);
}
function getCountSec(){
sec_left++;
document.getElementById("t2").innerHTML = "SECOND: " + sec_left;
}
function getZp() {
var inp1 = document.getElementById("in1").value;
var inp2 = document.getElementById("in2").value;
var summ = parseInt(inp1) + parseInt(inp2);
document.getElementById("t1").innerHTML = "SUMMA: " + summ;
}
</script>
</body>
</html>