I've added new room adjacent to my existing bed room, the old slab was extended about 2' outside the bed room as a shading. The company exposed the steel bars of the shading then bonded new bars and poured new slab integrated with the exposed bars. Is this the better way to do this job, is the new bond will be as it was if the two slabs was poured together or there will be a weak joint between the old and new slabs.

If you mean that the contractor chipped out concrete of the old slab and put the rebar of the new slab in the old one, that's as good as you can do. It's not quite a strong as if both slabs were poured at the one time but as good as you can do, and better than most would have done.

Yes hkstroud, that is exactly what I meant. How percent of strength had the concrete at the joint lost due to this process?