// usage inside a vm:
    var fooVM = function(){
        var self = this;
        var resource_uri = ko.observable('/api/v1/foo/');
        var bar = ko.observable(1);
        var baz = ko.observable(1);
        ko.saveOnChange(self,['bar']);
    }
    var f = new fooVM();
    f.bar(2);  // causes a PUT to /api/v1/foo/
    f.baz(2);  // doesn't do anything