{3: true, 4: true, 5: true, 6: true, 7: true}
[3,4,5,6,7]
var obj = {3: true, 4: true, 5: true, 6: true, 7: true};
var keys = Object.keys(obj);
console.log(keys);
var obj = {3: true, 4: true, 5: true, 6: true, 7: true};
var keys = [];
for(var k in obj) {
keys.push(k);
}
console.log(keys);