Vanity light installation question

Hi guys, I'd like to install a vanity light in our bathroom. The switch is wired and there's a junction box on the wall, the only problem is it's behind the mirror. Evidently the mirror was placed a little too high when the bathroom was renovated, so now it's covering the box, and moving the mirror lower is not an option because there's backsplash right below it. I understand that I can move the box up. I was wondering if instead I can install a new junction box above the old one (about 15-20 inches above), connect the fixture wires to a couple of connection wires and then push through the connection wires into the old box behind the wall and then connect them to the romex wire there. So basically the connection wires would be hanging behind the wall, but all the connections would be done inside the two boxes. Would something like this be considered safe/code? And if so, would using 14 AWG wires as connection wires be ok to do? This is a 15 amp circuit, but I'm not sure what gauge wires they used. Thanks in advance.

 

Best to abandon the box behind the mirror and move all the cables up to the new box if they come from above.

 

Run a new piece of cable from the old box up to the new location. Put a blank plate over the old box and hang the mirror .

Depending on fixture style, you may also need a box at the new location. Some fixtures act as the box.

 

Your best bet is the attic J-box. You can run new cable from there and place it exactly where you want.

If you planned on adding a 2' extension and then burying the box, yes that's not allowed, the box must remain accessible.