For Loop over Backbone Collection

Question

Fairly new to backbone, so this is a really basic question. I have a Backbone collection passed into a function and I can prove that it has been passed and that the models in the collection have ids.

Here's how I'm setting the ids -

convertToMapObjects: (results)  =>
   objectList = new ObjectList()
   results.each(result)->
    testObj = new TestObject()
    testObj.set
      id = result.get("id")
    objectList.add(testObj)

And in another function ( accessed through making the model trigger an event) -

getIds: (objects) =>
ids = (object.id for object in objects) 

I think the issue may be because of how I'm iterating through the collection because when I tried doing

for object in objects
   console.log(object)

I saw two undefineds. Is this correct? If so, why can't I use a for loop to go through a backbone collection? Also, is there a way I could do so?

Answer 1

A Backbone collection is not an array so for ... in won't produce the results you're expecting. You want to look at the collection's models property if you want to use a simple loop.

However, Backbone collections have various Underscore methods mixed in:

Underscore Methods (28)

Backbone proxies to Underscore.js to provide 28 iteration functions on Backbone.Collection. They aren't all documented here, but you can take a look at the Underscore documentation for the full details…

• forEach (each)
• ...

So you can use map or pluck if you'd like to avoid accessing the models property:

ids = objects.map (m) -> m.id
ids = objects.pluck 'id'

The pluck method is, more or less, just a special case of map but collections implement a native version rather than using the Underscore version so that they can pluck model attributes rather than simple object properties.

Answer 2

You want to loop over the models property of the collection, not the collection object itself.