Setting array value in backbone.js initialize function - backbone.js

Question

I'm trying to set an array value in a backbone.js model initialize function. In the line that starts with 'this.set...' I get a 'unexpected string' error. Is it not possible to set array values this way?
Thanks!
var bGenericItem = Backbone.Model.extend({
defaults: {
attrArray: new Array({'item_id': '', 'type': '', 'name':''})
},
initialize: function(){
// Set the id to cid for now
this.set({ attrArray["item_id"]: this.cid });
}
});

Answer 1

What you're trying to do doesn't make any sense. Your defaults is an array which holds a single object:
defaults: {
attrArray: [
{ item_id: '', type: '', name: '' }
]
},
You'd use an array if you wanted to hold a list of attribute objects. But, if you had a list of attribute objects, which one's item_id would you expect attrArray['item_id'] to refer to? Are you assuming that attrArray will always be initialized to the default value and that no one would ever send an attrArray in as part of your model's initial data? If so, you'd want something more like this:
// Use a function so that each instance gets its own array,
// otherwise the default array will be attached to the prototype
// and shared by all instances.
defaults: function() {
return {
attrArray: [
{ item_id: '', type: '', name: '' }
]
};
},
initialize: function() {
// get will return a reference to the array (not a copy!) so
// we can modify it in-place.
this.get('attrArray')[0]['item_id'] = this.cid;
}
Note that you'll run into some issues with array attributes that require special handling:
get('attrArray') will return a reference to the array that is inside the model so modifying that return value will change the model.
Things like a = m.get('attrArray'); a.push({ ... }); m.set('attrArray', a) won't work the way you expect them to, the set won't notice that the array has changed (because it hasn't, a == a is true after all) so you won't get "change" events unless you clone the attrArray somewhere between get and set.

Answer 2

There are several problems with your code
1: The defaults setting is an object literal which means the value that you assign to it is set as soon as it's defined. You need to set your defaults to a function, instead of a literal value. This will ensure each model instance gets it's own copy of the default values, instead of sharing a copy across every model instance.
2: You should also not use new Array, just use an array literal syntax []. But you're not really using an array in this code, so I removed the array wrapper for now.
3: You can't access attrArray directly. You must get it from the model's attributes and then update it
var bGenericItem = Backbone.Model.extend({
defaults: function(){
return {
attrArray: {'item_id': '', 'type': '', 'name':''}
};
},
initialize: function(){
// Set the id to cid for now
var arr = this.get("attrArray");
arr["item_id"] = this.cid;
}
});