how to add new item using knockout mapping plugin

Question

I'm trying out a knockout mapping sample and think I'm almost there. I don't seem able to add a new Foo to the viewModel.foos - can anyone see what I've missed here?

var Foo = function (data) {

    var self = this;
    self.id = data.id;
    self.Name = ko.observable(data.Name);

}

var dataMappingOptions = {
    key: function(data) {
        return data.id;        
    },
    create: function (options) {

        return new Foo(options.data);
    }
};


var viewModel = {

    foos: ko.mapping.fromJS([]),
    loadInitialData: function () {
        ko.mapping.fromJS(serverData, dataMappingOptions, viewModel.foos);
    },
    loadUpdatedData: function () {
        ko.mapping.fromJS(serverData, dataMappingOptions, viewModel.foos);
    }
};

viewModel.addFoo = function () {
    viewModel.foos.push(ko.mapping.fromJS(new Foo()));
    viewModel.loadUpdatedData();
}


    <ul data-bind="template: {name: 'TopTemplate'}"></ul>
<script type="text/html" id="TopTemplate">
    <li><span>Result</span>
        <ul data-bind=" template: {name:  'FooTemplate' , foreach: foos} " style="list-style-type:circle;margin-left:15px">
        </ul>
    </li>
    <button data-bind='click: addFoo'>Add Foo</button>
</script>       
<script type="text/html" id="FooTemplate">     
    <li><span data-bind='text: Name'></span>

    </li>

</script>

Answer 1

Since the original poster is applying observables inside the Foo class members there's no need to apply ko.mapping.fromJS to it. However I've found that when you have a 'raw' json object (with no mappings) that you need to add to an observable array (i.e. you have previously applied ko.mapping.fromJS()), you do actually need to perform ko.mapping.fromJS e.g.

myArray.push(ko.mapping.fromJS(myNewRawJsonItem));  

Otherwise your template bindings (if you have any) will complain that "TypeError xxxx is not a function".

Answer 2

You can just push a new Foo to your observableArray directly.

Here is a sample of loading some initial data and then loading some updated data along with a button to add new items on the client side. http://jsfiddle.net/rniemeyer/wRwc4/

var viewModel = {
    foos: ko.mapping.fromJS([]),
    loadInitialData: function() {
        ko.mapping.fromJS(initialData, dataMappingOptions, viewModel.foos);
    },
    loadUpdatedData: function() {
        ko.mapping.fromJS(updatedData, viewModel.foos);
    }
};

viewModel.addFoo = function() {
    viewModel.foos.push(new Foo({ id: 0, Name: "New" }));
};