JSFiddle - React, Tailwind, and code Playground

JavaScript

var collection = {
    zone1: ['placeA', 'placeB'],
    zone2: ['placeC', 'placeD']
};
    
function getZone(needle, collection) {
    var zones = Object.keys(collection),
        found;
    for (var i = 0, l = zones.length; i < l; i++) {
        found = collection[zones[i]].filter(function(place) {
            return needle == place;
        });
        if (found.length > 0) {
            return zones[i];
        }
    }
};

console.log(getZone('placeC', collection));