Hello,
So you want to solve this entirely in JS.. I assume you also have the coordinates or the stores in the JSON. The easiest approach would be to show stores in a radius of x km, then only show Y stores, ordered by distance (air distance). This solution would not require an address nor the use of a 'directions' service to get correct road distance to the client. Let's talk. The least I can do is point you in the right direction or answer some questions.