Conditional Synapse Embed

maybe_on.js

<script type="text/javascript">
var onswipeSometimes = function() {
  var usr = "f";
  var numToRedirect = 0.75; // percent of people to redirect
  var randomNumber = Math.random(); // [0, 1)
  if (randomNumber <= numToRedirect)  {
    var synapse = 'http://assets.onswipe.com/synapse/on.js?usr=' + usr;
    var embed = document.createElement('script');
    embed.setAttribute('type', 'text/javascript');
    embed.setAttribute('id', 'onswipe_synapse');
    embed.setAttribute('src', synapse);
    var parent = document.getElementsByTagName('head')[0];
    var first = parent.firstChild;
    parent.appendChild(embed, first);
  }
}();
</script>