var NUMBERS = 100;

​

function go() {

  var out = document.getElementById("output");

  for (var i = 1; i < NUMBERS+1; i++) {

    addSpan(i);

  }

  function hover(id, color, size) {

    var span = document.getElementById(id);

    span.style.backgroundColor = color;

    span.style.fontSize = size;

  }

​

  function addSpan(i) {

    var span_one = document.createElement("span");

    span_one.id = "span" + i;

    span_one.innerHTML = "" + i;

    out.appendChild(span_one);

    if (isPrime(i) === true) {

      span_one.style.backgroundColor = "red";

      span_one.onmouseover = function() {

        hover("span"+i, "yellow", "150%")

      };

      span_one.onmouseout = function() { 

        hover("span"+i, "red", "100%");

      };

    }

  }

}

​

​

function isPrime(i) {

  return true;

}

​

go();