如何使用knockout mapping插件添加新项目

var ViewModel = function() {
    var self = this;
    self.items = ko.observableArray([]);
    self.newItem = ko.observable('');

    self.addItem = function() {
        if (self.newItem().length > 0) {
            self.items.push({ name: self.newItem() });
            self.newItem('');
        }
    };
};

var viewModel = new ViewModel();
var data = {
    items: [
        { name: 'Item 1' },
        { name: 'Item 2' }
    ],
    newItem: ''
};

ko.mapping.fromJS(data, viewModel);
ko.applyBindings(viewModel);

<div>
    <ul data-bind="foreach: items">
        <li data-bind="text: name"></li>
    </ul>
   <input type="text" data-bind="textInput: newItem" placeholder="New item">
   <button data-bind="click: addItem">Add item</button>
</div>