Further to Bob9f's comment, this is my variation on JK's original door catch. He made them slightly differently to this, but I reckon this is an improvement on the original. If there are a pair of doors, an 'upstand' can be incorporated to keep the doors closed flush on the outside. A single door will close against the side of the cabinet.
As the catch forces the door upwards slightly, a small 'button' needs to be turned which is equal to the shadow gap made when the door(s) is fitted. This is fiddly to do, but easy to adjust 'in situ' with a smoothing file and 320g sandpaper block.
The following pics show a roughed out catch made some time ago which was never used. Something hard and nasty is ideal for these little catches so I usually use Indian ebony or African Black Wood; this one's is made form an oddment of rosewood.
You can see from the side pic that the bit that engages on the underside of the door is slightly domed and the easiest way to do this is with needle files and sandpaper to finish.
On the underside, beneath the 'dome' a chopped down biro spring is fitted which fits into a hole. There's another shallow hole also drilled into the carcase, so the spring is secure and not liable to ping off into the deepest and darkest recesses of the 'shop
The spring shown is fairly chunky and quite powerful...too much in fact, so biro springs are ideal
The first time you make these things, they are incredibly fiddly. Slots are machined with a router cutter and the blank is carefully disc sanded to make a slopy-ish fit. The clearance hole for the screw should also enable a small amount of vertical movement; if it's too tight the catch won't move. I've made so many now that I can knock one out in around 20 minutes - Rob