test.js

function B1() {
  /* Benchmark.prototype.setup goes here {{{ */
  var arr1 = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10],
      seed_data = 3,
      result = 0;
  /* }}} */
  var start = new Date;
  while (...) { /* do N iterations of test body */
    /* body of the case goes here {{{ */
    for (var i = 0; i < arr1.length; i++) {
      result += (seed_data * i);
    }
    /* }}} */
  }
  var end = new Date;
  /* N / (end - start) gives ops per ms result */
}

function B2() {
  /* Benchmark.prototype.setup goes here {{{ */
  var arr1 = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10],
      seed_data = 3,
      result = 0;
  /* }}} */
  var start = new Date;
  while (...) { /* do N iterations of test body */
    /* body of the case goes here {{{ */
    var l = arr1.length;
    for (var i = 0; i < l; i++) {
      result += (seed_data * i);
    }
    /* }}} */
  }
  var end = new Date;
  /* N / (end - start) gives ops per ms result */
}

function B3() {
  /* Benchmark.prototype.setup goes here {{{ */
  var arr1 = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10],
      seed_data = 3,
      result = 0;
  /* }}} */
  var start = new Date;
  while (...) { /* do N iterations of test body */
    /* body of the case goes here {{{ */
    var arr2 = [1, 2, 3, 4, 5, 6, 7, 8, 9];

    for (var i = 0; i < arr2.length; i++) {
      result += (seed_data * i);

      if (i === 4) {
        arr2.push(10)
      }
    }
    /* }}} */
  }
  var end = new Date;
  /* N / (end - start) gives ops per ms result */
}

Awesome! Thanks for help me to find the right case.