AB test a new JS feature

new-feature-testable.js

var should_show = $.cookie('testNameSpace');

// Allow A/B test override.
if ($('body.override').length > 0) should_show = 1;

// User is a yes OR no choice yet.
if (should_show == 1 || (should_show == null && Math.random() < 0.2)) {
  //Set cookie to yes.
  $.cookie('testNameSpace', 1, { path : '/' });

  thingToTest();
}
else {
  // Hide form untested users.
  $.cookie('testNameSpace', 0, { path : '/' });
}