Optionally compute field only on attribute get

[jd-boyd]

I am using backbone-computedfields for a referenced object. However, I am loaded the referenced object on demand, it isn't a pre-loaded set.

I would like for the computed field to not be calculated until its attributed is gotten with a get call. I picture this being set with a lazy key in the options dictionary for the computed field.

    computed: {
        grossPrice: {
            depends: ['netPrice', 'vatRate'],
            get: function (fields) {
                return fields.netPrice * (1 + fields.vatRate / 100);
            },
            lazy: true
    }

[JSteunou]

You can already to it by using a function as dependency

In this function listen to when netPrice is set then listenTo its change.

Or maybe you could just set a default value for netPrice (null or undefined) and make grossPrice be null or undefined accordingly.