[Vlasenko Fedor]

С помощью eval и регулярных выражений

<div id="test"></div>
<script>
  window.onload = function () {
    var txt = "Hi-<script>alert('HI!'); <" + "/script>hi \
        	   Ha-<script>alert('HA!'); <" + "/script>ha";
    test.innerHTML = txt.replace(/<script>(.*?)<\/script>/ig, function (a, b) {
      eval(b);
      return a;
    });
  }
</script>