code: function indexOf(arr, value, start) {
    start = start || 0;
    if (arr == null) {
      return -1;
    }
    var len = arr.length;
    var i = start < 0 ? len + start : start;
    while (i < len) {
      if (arr[i] === value) {
        return i;
      }
      i++;
    }
    return -1;
  }
docs: Custom `indexOf` implementation that works with sparse arrays
  to provide consisten results in any environment or browser.
  
  @param  {Array} `arr`
  @param  {*} `value`
  @param  {Array} `start` Optionally define a starting index.
  @return {Array}