code: function unique(arr) {
    var ret = [];
  
    for (var i = 0; i < arr.length; i++) {
      if (~ret.indexOf(arr[i])) continue;
      ret.push(arr[i]);
    }
  
    return ret;
  }
docs: Return unique array.
  
  @param {Array} arr
  @return {Array}
  @api private