How do I deep copy in javascript?

Question

I have a situation similar to what you see below. The variable id is set to '03' before the first asynchronous callback is returned. Is there a way to deep copy, or "close" around the variable like you can with blocks in Objective-C? Is there a best practice?

var ids = ['01', '02', '03'];

for(var i=0, i < ids.length; i++){
  var id = ids[i];
  collection.find({id: ids} function () {
    console.log(id);
  });
}

The console output is:

03
03
03

Answer 1

There are several ways to do it. One is to iterate with a a method that uses a closure as a callback.

ids.forEach(function (elem) {
    collection.find({id: ids} function () {
        console.log(elem);
    });
});