setInterval in javascript no sum

Question

Good, I have the following javascript code and when I try to add the strMessage it does not add up, but adds side by side to the value and so on each time it runs, which I am doing wrong?

function main() {

  var s = 0;
  //Espera um segundo
  setInterval(function() {

$.ajax({
  url: 'teste3.php',
  success: function(strMessage) {

    s += strMessage;
  },
});

document.write(s);

  }, 1000);
}

window.onload = main;

Answer 1

maybe you would have to make strMessage a number in javascript

s += parseInt(strMessage); 

or to decimal places:

parseFloat()