What is the proper way to save data in a component in Lightning?

Question

Let's say I have a Lightning component client side controller that does some calculation on initialization based on attributes that were set but it isn't going to be rendered it's just internal information about the component. I don't want to create an attribute in the markup I just want to save it for later access in event handlers. What's the proper way to do that? I'm thinking something like this but there doesn't seem to be any documentation about it.

({
  doInit : function(cmp, event, helper) {
     var c = cmp.get("v.a") + cmp.get("v.b");
     cmp.setData("c",c);
  }
})

As a side not there is very little documentation on the javascript objects that are available and their usage in the lightning docs. Thanks for any help!

Answer 1

I would highly recommend an attribute. However, you can store things on the helper if you really really want to. This is probably not a best practice, and might cause breakage or be unreliable.

Think of this like a global static variable, it's not tied to an instance of your component.

Helper:

({
  c : {},
  doInit : function(cmp, event) {
     var c = cmp.get("v.a") + cmp.get("v.b");
     this.c = c;
  }
})

When you mutate this.c, you're actually manipulating the definition of your helper, not the instance of your component, so any other components of the same type should also see that value in this.c.