function indexOf (arr, o, i) {
    if (Array.prototype.indexOf) {
      return Array.prototype.indexOf.call(arr, o, i);
    }

    if (arr.length === undefined) {
      return -1;
    }

    for (var j = arr.length, i = i < 0 ? i + j < 0 ? 0 : i + j : i || 0
        ; i < j && arr[i] !== o; i++);

    return j <= i ? -1 : i;
  }
Array indexOf compatibility.

@see bit.ly/a5Dxa2
@api public