using json object with lots of properties instead of arrays - arrays

Question

instead of an array:
var arrayExample = {
"lotsOfStuff" : [
{"id" : "th1", "name" : "thing1", "type": "thing", "moo":"a"},
{"id" : "th2", "name" : "thing2", "type": "thing", "moo":"z"},
{"id" : "th3", "name" : "aDifferentThing3", "type": "differentThing", "moo":"m"}
]
}
Use lots of properties:
var propertyExample = {
"lotsOfStuff" : {
"id1" : {"name" : "thing1", "type" : "thing", "moo" : "a" },
"id2" : {"name" : "thing2", "type" : "thing", "moo" : "z" },
"id3" : {"name" : "aDifferentThing3", "type" : "differentThing", "moo" : "m" }
}
}
can still iterate through them
for(var idx in arrayExample.lotsOfStuff) {
var thing = lotsOfStuff[idx];
var id = thing.id;
...
}
and
for(var id in propertyExample) {
var thing = lotsOfStuff[id];
...
}
but you have the bonus of a lookup by id at the expense of the lookup by index position
Any problems with using this array alternative??
what about performance with lots of elements??

Answer 1

If the order of the elements matters, use an array.
If you need to look up by ID, use an object.
If you need to do both, create both an array and an object whose elements point to the same objects.
Accessing object properties is probably slower than accessing array elements, because it requires hashing instead of simple indexing. But if you need to look up by ID in an array, that will require a linear search, which is much slower than hashing if there are lots of elements. The performance of objects should not be impacted significantly by the number of elements.