[monolithed]

Хм.

describe('Array#copyWithin', function() {
      it('has the right arity', function() {
        expect(Array.prototype.copyWithin.length).to.equal(2);
      });

      it('works with 2 args', function() {
        expect([1, 2, 3, 4, 5].copyWithin(0, 3)).to.eql([4, 5, 3, 4, 5]);
        expect([1, 2, 3, 4, 5].copyWithin(1, 3)).to.eql([1, 4, 5, 4, 5]);
        expect([1, 2, 3, 4, 5].copyWithin(1, 2)).to.eql([1, 3, 4, 5, 5]);
        expect([1, 2, 3, 4, 5].copyWithin(2, 2)).to.eql([1, 2, 3, 4, 5]);
      });

      it('works with 3 args', function() {
        expect([1, 2, 3, 4, 5].copyWithin(0, 3, 4)).to.eql([4, 2, 3, 4, 5]);
        expect([1, 2, 3, 4, 5].copyWithin(1, 3, 4)).to.eql([1, 4, 3, 4, 5]);
        expect([1, 2, 3, 4, 5].copyWithin(1, 2, 4)).to.eql([1, 3, 4, 4, 5]);
      });

      it('works with negative args', function() {
        expect([1, 2, 3, 4, 5].copyWithin(0, -2)).to.eql([4, 5, 3, 4, 5]);
        expect([1, 2, 3, 4, 5].copyWithin(0, -2, -1)).to.eql([4, 2, 3, 4, 5]);
        expect([1, 2, 3, 4, 5].copyWithin(-4, -3, -2)).to.eql([1, 3, 3, 4, 5]);
        expect([1, 2, 3, 4, 5].copyWithin(-4, -3, -1)).to.eql([1, 3, 4, 4, 5]);
        expect([1, 2, 3, 4, 5].copyWithin(-4, -3)).to.eql([1, 3, 4, 5, 5]);
      });

      it('works with arraylike objects', function() {
        var args = (function () { return arguments; }(1, 2, 3));

        expect(Array.isArray(args)).not.to.be.ok;

        var argsClass = Object.prototype.toString.call(args);
        expect(Array.prototype.slice.call(args)).to.eql([1, 2, 3]);

        Array.prototype.copyWithin.call(args, -2, 0);

        expect(Array.prototype.slice.call(args)).to.eql([1, 1, 2]);
        expect(Object.prototype.toString.call(args)).to.equal(argsClass);
      });
    });

copyWithin: function(target, start) {
        var end = arguments[2]; // copyWithin.length must be 2
        var o = ES.ToObject(this);
        var len = ES.ToLength(o.length);

        target = ES.ToInteger(target);
        start = ES.ToInteger(start);

        var to = target < 0 ? Math.max(len + target, 0) : Math.min(target, len);
        var from = start < 0 ? Math.max(len + start, 0) : Math.min(start, len);

        end = (end===undefined) ? len : ES.ToInteger(end);

        var fin = end < 0 ? Math.max(len + end, 0) : Math.min(end, len);
        var count = Math.min(fin - from, len - to);
        var direction = 1;

        if (from < to && to < (from + count)) {
          direction = -1;
          from += count - 1;
          to += count - 1;
        }

        while (count > 0) {
          if (_hasOwnProperty.call(o, from)) {
            o[to] = o[from];
          }
          else {
            delete o[from];
          }

          from += direction;
          to += direction;
          count -= 1;
        }

        return o;
}