code: function(el, fromIndex /* = @[*-1] */){
        var O      = toIObject(this)
          , length = toLength(O.length)
          , index  = length - 1;
        if(arguments.length > 1)index = Math.min(index, toInteger(fromIndex));
        if(index < 0)index = toLength(length + index);
        for(;index >= 0; index--)if(index in O)if(O[index] === el)return index;
        return -1;
      }
docs: 22.1.3.14 / 15.4.4.15 Array.prototype.lastIndexOf(searchElement [, fromIndex])