stress.js

var stress = function(fn, iterations) {

  iterations = iterations || 1;
  var result;
  var start = new Date();

  for (var i = 0; i < iterations; ++i) {
    result = fn();
  };

  var end     = new Date();
  var total   = end - start;
  var average = total / iterations;

  return {
    iterations: iterations,
    total: total + 'ms',
    average: average + 'ms',
    result: result
  };
};